Characterization and High-Temperature Oxidation Behavior of Ni–20Cr Deposits Fabricated by Cold Spray-Based Additive Manufacturing

Abstract

Hot corrosion is a critical problem in a wide range of high-temperature applications. Ni–20Cr alloy is frequently used in such applications owing to its good hot-corrosion resistance. In the current work, thick Ni–20Cr plates in a thickness range of 6–10 mm were fabricated using cold spray-based additive manufacturing (CSAM). High-pressure cold spraying was used with nitrogen as the propellant gas. Pre- (substrate heating, SH) and post-heat treatments (hot isostatic pressing, HIP) were also performed to comprehend the changes in the deposit properties. The deposits were subjected to microstructural and mechanical characterization to explore the potential of cold spraying for CSAM of Ni–20Cr standalone products. The cold-sprayed plates were successfully developed without any oxide formation. HIP treatment was found to be useful to reduce porosity. The cold-sprayed substrate-heated Ni–20Cr deposits exhibited excellent oxidation resistance at a high temperature of 900 °C.

1. Introduction

Due to their promising high-temperature properties, Ni–20Cr alloys are frequently used for various applications in several industries such as automobile, aerospace, energy, nuclear, marine, and electronic industries [1,2,3,4]. Moreover, future applications of the alloys may include developing 3D standalone components for real-time industrial usage in energy and electricity (bolts, blades, shafts, discs, exhaust gas reheaters, rings of gas, and steam turbines); nuclear (catheters, control levers, stem); automotive (exhaust valves, engine fasteners, liners, piston rings); metal processing (heating tools, molds); national defense and aerospace (shafts, blades, afterburners, barrels, thrust reversers for jet turbine engines); electronics (electronic components, vacuum tube components) [5]. Products of Ni–20Cr materials are generally manufactured using various conventional methods such as conventional powder metallurgy, liquid metallurgy, casting, forging, and machining [6]. However, in the pursuit of achieving sustainability and economy in manufacturing, several other routes are under consideration for the manufacturing and repair of Ni–20Cr components, some of which include thermal spray methods namely high-velocity oxy-fuel (HVOF), plasma spray, D-Gun, and laser-assisted routes [7,8,9,10,11,12,13]. These routes/methods often lead to high porosity and in-flight oxidation, non-uniformity, interfacial diffusions, and residual and thermal stresses. Recently, cold spray-based additive manufacturing (CSAM) has evolved as a potential solid-state manufacturing process, in which feedstock powder material is deposited layer-by-layer by accelerating and impacting it onto some substrate to develop thick plates or free-standing components of pure metals, alloys, and composites [14,15]. Since there is no powder particle melting during CSAM, the final products have lower thermal (tensile) stresses, no oxide formation, and marginal (undesirable) interfacial diffusions. These advantages make CSAM a potential technique to fabricate standalone products and repair components [16,17]. However, there are numerous issues that make it difficult to employ CSAM for material deposition in bulk. Typically, the size of the plume leaving the convergent–divergent (CD) nozzle determines the dimensions of the sprayed features. Additionally, each single cold spray pass has a distinctive shape on account of the material distribution exiting the nozzle, which affects the ultimate geometry of the deposits, especially when the cold spray nozzle is continuously maintained at a right angle to the substrate plate. As a result, geometrical correctness is a vital aspect of CSAM. Greater concern for the developed feature is raised by higher porosity in between layers. Hence, knowledge of optimizing tool paths and kinematics of robots is very critical in overcoming these issues of geometric inaccuracies and porosity [18]. In a nutshell, the process appears to be promising; however, the applicability of the cold spray process for components at an industrial length-scale in sectors such as energy, aviation, oil and gas, locomotives, healthcare, etc., is not well known. Moreover, understanding the significance of process parameters on the microstructure evolution and mechanical behavior, as well as degradation behavior under simulated operating conditions, is critical for advancing this technology [16,19]. In this context, work related to CSAM of Ni–20Cr alloys is limited, whereas the application domains of these alloys are numerous. The main goal of this work is to develop a knowledge base on CSAM of Ni–20Cr alloy thick deposits, which shall form the basis for the manufacturing of Ni–20Cr standalone parts for industrial use. To achieve this prime objective, the microstructural studies and mechanical characterization of the cold-sprayed Ni–20Cr deposits have been performed to establish structure–property relationships. The effect of pre- and post-processing techniques on the properties of cold-sprayed Ni–20Cr samples has also been evaluated.

2. Methodology

The feedstock material was commercially available Ni–20Cr powder with a particle size in the range of 5–45 µm (Praxair Surface Technologies, Indianapolis, IN, USA). The substrate material used was IN718 superalloy. A cold spray (CS) system (Sulzer Metco) was used to manufacture the Ni–20Cr plates (referred to as deposits or samples also). The CS system includes a spray gun having a convergent–divergent nozzle and a gas pre-heater, powder feeder, gas control unit, and associated peripherals. The robotic arm is employed to plan the trajectory of the cold spray gun as per the requirement. The details of the cold spraying process parameters and pre-/post-heat treatments conducted on the CSAM deposits are given in Table 1.

These cold-sprayed samples were prepared at General Electric (Bengaluru), India. The designation system for the sample is given in Table 2. The schematics of the pre-/post-heat treatment operations carried out on respective samples are also shown in Figure 1. The experiment flowchart followed during the course of the study is given in Figure 2.

A scanning electron microscope (SEM) (JEOL JSM-6610LV, JEOL Ltd., Tokyo, Japan) was used to examine the cross-sectional morphology of the CSAM deposits in order to comprehend the microstructure and also to spot oxide inclusions, pores, unmelted particles, etc. The conventional metallographic sample preparation protocols were used for the preparation of samples.

The calculation of the percentage of apparent surface porosity and pore size distribution in all the samples was performed using Image-J tool which is an open-source image analysis software. Ten random SEM (greyscale) images for each of the samples were used in Image-J for the analysis. The procedure includes several steps such as converting SEM images to bmp or tiff format, introducing and setting scale to software, binarization using the thresholding procedure, and analyzing the results for determining the pore size distribution and percentage of apparent surface porosity. For the determination of the different phases in the deposits, X-ray diffraction (XRD) (Analytical X-pert Pro, Almelo, The Netherlands) analysis was conducted. The diffraction patterns were obtained using a diffractometer equipped with a nickel filter and operated at a voltage value of 35 kV and a current of 20 mA with Cu-Kα radiation. The intensities were measured using a goniometer at a speed of 1°/min whereas the samples were examined at 1 kcps scanning speed with an angular 2θ range of 10 to 100°. The application software for X-ray diffraction is interfaced with the diffractometer and delivers “d” values for each diffraction peak. These “d” values are then used to categorize different phases. Small samples were sectioned from the developed deposits for bulk density measurements in g/cc. For the purpose of calculating the volume, the dimensions of these dissected samples were measured using Vernier calipers, while the weights were recorded using an electronic balance with a sensitivity of 10⁻³ g. The apparent density was determined using an Archimedes principle-based density measuring kit (Mettler Toledo, MS-DNY-54, Zürich, Switzerland). Microhardness measurements were performed using microhardness testing equipment (Wilson, 402MVD, Chicago, IL, USA) with a 300 g load and a 10 s dwell period. Five consecutive lines of indents in a lateral direction to the samples were made and the mean of ten values was considered. Quasistatic nanoindentation was performed, which is the standard technique used for the nanomechanical characterization of materials. A Triboindenter (Hysitron, Inc., TI-950, Minneapolis, MN, USA) was employed to determine the value of nanohardness and Young’s modulus of the manufactured plates at the surface and along their thickness. The Oliver–Pharr method was used for the interpretation of the nanoindentation data [20]. Twenty indentations in the shape of a 5 by 4 matrix were formed on the surface with an inter-indent interval of 5 μm. To determine the average values, this experiment was carried out three times. The test was carried out with a typical Berkovich diamond tip indenter (three-sided) under a steady loading of 1000 μN. The indenter had a Poisson’s ratio and an elastic modulus of 0.07 and 1140 GPa, respectively. The specimens drawn from the Ni–20Cr thick plate samples were also subjected to tensile testing (thrice for each of the samples) on a universal tensile testing machine (FIE, UTES 40, Kolhapur, Maharashtra, India). Using an EDM wire cut machine, dog bone shaped (in accordance with ASTM standards E8) specimens with 25 mm gauge length, 10 mm width, and 1 mm thickness were generated from deposited Ni–20Cr with various pre- and post-heat treatments. The samples were evaluated using a load cell with a maximum capacity of 20 kN and a small strain rate having a value of 0.02 mm/min. Material strain is detected from the machine’s crosshead displacement with a digital indication having 0.001 mm resolution and a maximum displacement of 25 mm, which is linked to a PC via an interface.

High temperature oxidation investigations were performed on cold-sprayed substrate-heated deposits in a SiC tube furnace at 900 °C. The furnace was successfully calibrated to a certainty level of ±5 °C by using a Platinum/Platinum-13% Rhodium thermocouple. The cold-sprayed substrate-heated deposit was polished using the standard metallographic techniques as explained earlier. The physical dimensions of the sample were determined with the help of Vernier calipers to calculate the total surface area. After that, the samples were washed with isopropyl alcohol and then hot-dried to eliminate the residual moisture. The sample was placed in an alumina boat during the experiment, and the aggregate weight of the boat and the sample was quantified. It was presumed that the weight of the alumina boat would remain unchanged during the entire cyclic oxidation study because these were preheated for a duration of 6 h at a constant temperature of 1200 °C. The specimen-containing boat was then placed inside the furnace hot zone, which was preheated to 900 °C. The sample was kept in the furnace for one hour in still air before being removed and cooled to room temperature for an interval of 20 min, respectively. The combined weight was thus measured. This constituted one cycle of cyclic oxidation at high temperatures. For the weight change measurements, any spalled scale in the boat was also taken into account. The weight was determined using an electronic balance with a 10⁻³ g sensitivity. The color, luster, or any other change in the physical characteristics of the oxide scales were observed visually after each cycle.

3. Result and Discussion

3.1. Microstructural Analysis

SEM and EDS investigation of the powder feedstock showed its spherical morphology and oxide-free surface (With 77% Ni and 23% Cr) as represented in Figure 3 and Figure 4, respectively. XRD study (Figure 5) also showed the absence of oxides and supported the EDS analysis. A mixture of nickel and chromium with Ni₃Cr phases was observed.

Macrographs of the developed Ni–20Cr thick plates along with thickness are shown in Figure 6. All of these deposits got detached from the substrate while sectioning the plates using a wire-EDM process. This may be due to poor adhesion, which is actually required to easily obtain standalone deposits. Standalone thick plates were characterized to evaluate the effects of substrate heating and HIP treatment on their properties. XRD analysis of all the specimens showed no-oxide formation. Only the Ni₃Cr phase was observed. However, the shifting of peaks towards a lower diffraction angle for Ni–20Cr-AS was observed. Peak shifts can be caused by changes in chemical composition or by strain [21]. Since the chemical composition remained unchanged, the only other possibility for peak shifting is strain. This might have been caused by residual stress from high-velocity particle impact deformation in the cold-sprayed deposits [22]. The shifting observed was towards a lower diffraction angle, suggesting that the stresses/strains might be compressive in nature [22]. Moreover, peak broadening of the Ni–20Cr-SH deposit was observed, which depicted the grain refinement or recrystallization of the deposited material. As the high-velocity particles strike the heated substrate, they become deformed, resulting in dynamic recrystallization and a refined grain structure leading to peak broadening in the XRD analysis [23].

Cross-sectional SEM images of Ni–20Cr-AS, Ni–20Cr-SH, and Ni–20Cr-HIP have been represented in Figure 7a, Figure 7b, and Figure 7c, respectively. Moreover, the comparison of density, apparent surface porosity, and pore size distribution has been represented in Figure 8. The pores/voids were large in numbers, and size was of the order of 2–10 µm in the Ni–20Cr-AS (Figure 7a), which resulted in 9.54% apparent surface porosity (calculated from Image-J analysis) and lesser density of the magnitude of 6.43 g/cc (calculated by Archimedes principle using density measuring kit) as compared to the density of bulk Ni–20Cr alloy (8.3 g/cc). Comparatively smaller pores of the order of 1–3 µm have been observed in Ni–20Cr-SH (Figure 7b) with 6.36% apparent surface porosity. The density of the sample (7.36 g/cc) was observed better than Ni–20Cr-AS but lesser than the bulk material. However, a surface with the least defects (porosity and voids) was observed for Ni–20Cr-HIP samples (as represented in Figure 7c). The least apparent surface porosity having a value of 2.43% and the best density of the order of 8.14 g/cc were achieved with HIP treatment. A pore size in the range of 1–4 µm was observed as comparatively bigger than Ni–20Cr-SH. It can be perceived from Figure 7 and Figure 8 that HIP treatment improved the microstructure by reducing the porosity and improving the density by 75% and 27%, respectively. EDS spectra of Ni–20Cr-AS, Ni–20Cr-SH, and Ni–20Cr-HIP deposits are represented in Figure 9a, Figure 9b, and Figure 9c, respectively. There is a small difference in the elemental compositions of all three samples that might be due to some measurement error. The elemental composition showed the absence of oxygen and the presence of a mixture of nickel and chromium in all the deposited specimens. The same has also been supported by XRD analysis as represented in Figure 5.

3.2. Mechanical Behavior

The microhardness, nanohardness, and elastic modulus of Ni–20Cr-AS, Ni–20Cr-SH, and Ni–20Cr-HIP deposits are displayed in Table 3.

The average microhardness of Ni–20Cr-SH was observed to be the highest among the investigated cases, with the least variations (highest = 432 HV, lowest = 412 HV). Moreover, Ni–20Cr-AS deposits showed higher variations in hardness (highest = 439 HV, lowest = 339 HV). Ni–20Cr-HIP deposits showed the lowest hardness among the investigated cases with moderate variations. These variations in microhardness can be related to the porosity observed. Ni–20Cr-AS has the highest apparent surface porosity, hence resulting in higher hardness variations as compared to the other two deposits. The Ni–20Cr-HIP sample has the least apparent surface porosity compared to the other two deposits, hence resulting in the least variations in hardness values. Moreover, the nanohardness of Ni–20Cr-HIP was observed to be the lowest, whereas it was the highest for Ni–20Cr-AS deposits. It is worth mentioning that the elastic modulus of all the Ni–20Cr deposits was found to be closer to that of the Ni–20Cr bulk material (214 GPa) [24], which is a desirable attribute for the cold spray process to qualify as an additive manufacturing approach. The load-displacement curves were plotted for all the cases using the data obtained from the nanoindentation testing and represented in Figure 10. Ni–20Cr-SH was found to be harder and stiffer while Ni–20Cr-HIP was observed to be softer and more plastic of all the three Ni–20Cr cold sprayed deposits. The Ni–20Cr-AS deposit showed moderate characteristics. Therefore, the results obtained from the microhardness (Table 3) were validated through load-displacement curves. The decrease in hardness due to HIP treatment was observed as residual compressive stresses are released. Moreover, the HIP time period of 2 h at 900 °C might have resulted in recovery, recrystallization, and grain growth of the Ni–20Cr deposits [25]. Therefore, the lowest values of microhardness and nanohardness were observed. On the other hand, it is believed that the grain was refined in Ni–20Cr-SH deposits on account of static recrystallization, which might have resulted in increased hardness, as per the well-known Hall–Petch effect. It is worth mentioning that for Ni–20Cr-SH cases, the substrate temperature is higher during cold spraying as HVOF (high-velocity oxy-fuel) gun is also being traversed alongside the cold spray gun for the purpose of substrate heating. This heating ensures enhanced deformation of already deposited powder particles. It is reported that such additional deformation would lead to more nucleation sites for recrystallization which further induces grain refinement [26]. Moreover, elongated and distorted grains in Ni–20Cr-AS showed high hardness compared to Ni–20Cr-HIP on account of mechanically induced grain refinement [27].

The engineering stress vs engineering strain curves of Ni–20Cr-AS, Ni–20Cr-SH, and Ni–20Cr-HIP deposits are represented in Figure 11. The comparison of macro tensile results of all cold-sprayed Ni–20Cr deposits with bulk material properties of Ni–20Cr is represented in Table 4. The UTS (ultimate tensile strength) was observed highest (nearest to bulk) for the Ni–20Cr-SH deposit with a moderate percentage of elongation. However, the highest percentage of elongation with the lowest UTS was observed for Ni–20Cr-HIP. The percentage elongation of the Ni–20Cr-HIP is equal to the percentage elongation of the bulk Ni–20Cr [24,28]. Ni–20Cr-AS showed moderate UTS with the least percentage of elongation. It is worth mentioning that the elastic modulus and yield strength of Ni–20Cr-SH deposits are nearest to that of the bulk Ni–20Cr alloy. The lesser yield strength of Ni–20Cr-AS may be due to the porosity, owing to which the crack initiation might have started at a lesser stress leading to lower UTS and percentage of elongation. However, the effect of grain refinement and recrystallization in Ni–20Cr-SH dominated over the porosity effect, hence resulting in better UTS and percentage of elongation as compared to Ni–20Cr-AS. Similarly, the higher modulus in Ni–20Cr-SH deposit may be due to the recrystallization (grain refinement), whereas the lowest elastic modulus of Ni–20Cr-HIP may be due to grain growth after recrystallization during HIP treatment [25,26]. Therefore, Ni–20Cr-SH may have a greater number of grain boundaries to pile up the dislocations and lesser volume for their movement (gliding) as compared to the lesser number of grain boundaries of Ni–20Cr-HIP and more volume for their movements [29]. Hence, it resulted in more ductility, lesser elastic modulus, and yield strength for Ni–20Cr-HIP and vice-versa for the Ni–20Cr-SH case. Moreover, the elastic modulus values obtained with nanoindentation analysis were observed as comparatively higher than the values obtained from macro-tensile testing. This mismatch may be primarily explained by the application of Oliver and Pharr’s technique, which is based on Sneddon’s analysis of elastic contact [20,30]. The lateral stresses produced by the indentation process are not taken into consideration by the effective elastic modulus (E_eff), which is solely influenced by the elastic modulus of the material in the indentation direction. Through the parameter, which is shown in the following equation, this stress mechanism results in an overestimation of the elastic modulus.

(1)$E_{eff}=\frac{1}{\beta }\frac{\sqrt{\pi }}{2}\frac{S}{\sqrt{A\left(h_c\right)}}$

where $\beta$ is equal to 1.034 for a Berkovich indenter, S is the contact stiffness, and A(h_c) is the contact area [31,32,33].

3.3. High-Temperature Cyclic Oxidation

It was observed from the initial characterization results that Ni–20Cr-SH has the best properties approaching the bulk material among all the investigated cases. Therefore, to study its sustainability at high temperatures, a cyclic oxidation study for the Ni–20Cr-SH deposit was performed. The weight change data for the deposit are given in Figure 12 and Figure 13, which establish that the weight loss has shown a tendency to become stabilized with minor deviations. However, the overall weight loss by the sample at the end of the 50th cycle has been observed as marginal (3.684 mg/cm²), which demonstrates its stability at high-temperature applications.

After each oxidation cycle, visual inspections were performed, and variations in color, luster, adherence spalling tendency, and crack propagation were documented. The exposed samples were thoroughly examined after the end of the 1st, 4th, 27th, 38th, 46th, and 50th cycles. Their macrographs were then obtained and are shown in Figure 14. The samples at the start were slightly green and as the cycles progressed, they turned bluish-green.

It can be observed from the macrographs that after the 50th cycle, a blister has formed on the sample surface. The observed color changes and minor weight gains and losses (deviations) indicate the formation and evaporation of phases during oxidation.

Further, the SEM, EDS, and XRD analyses of Ni–20Cr-SH deposits subjected to high-temperature cyclic oxidation in air at 900 °C for 50 cycles, are displayed in Figure 15, Figure 16, and Figure 17, respectively. The SEM image shows an irregular and rough surface with a disintegrated oxide scale morphology. The EDS mapping showed the existence of Ni, Cr, and O on the entire surface scale. Further, the XRD data showed a mixture of CrNi₃ and CrO₃ phases in the oxide scales. The phase of chromium with oxygen (CrO₃) is volatile in nature. The outer layer of chromia (Cr₂O₃) formed during the cyclic oxidation of the Ni–20Cr-SH sample evaporates owing to its conversion leading to deviations in weight. According to the differential equation that quantifies the oxidation kinetics and the analysis of the mass gain curves obtained using thermogravimetry after 50 cycles, the formation of Cr₂O₃ results in a small weight gain, whereas the converted phase’s evaporation (due to its volatile nature) results in a small weight loss [34,35]. The weight change has been observed as marginal; therefore, the Ni–20Cr-SH deposits can be sustained in high-temperature environments for a longer time.

4. Conclusions

The cold spray-based additive manufacturing (CSAM) process could be successfully used to develop plates of Ni–20Cr in the thickness range of 6–10 mm with properties akin to bulk Ni–20Cr alloy. The study establishes the viability of the CSAM process to develop standalone products of Ni–20Cr material, provided the cold spray gun can be manipulated by a robotic arm to follow the path required to develop/deposit such geometries, which is quite feasible with the current state-of-the-art robotic manipulators. Moreover, the results of the study suggest two possible interventions, namely substrate pre-heating (SH) and hot isostatic pressing (HIP) post-treatment to tune the properties of the deposits. Each of these treatments improves specific properties in the deposits, and a suitable treatment may be used as an option to achieve desirable properties based upon the application of the product; for instance, if better tensile strength is needed, SH will be more suitable to supplement the cold spray process, whereas if more ductility with lesser porosity is needed, HIP could supplement the cold-sprayed deposits. This study confirms the fact that cold spray additive manufactured products have the potential to replace their counterpart products fabricated by conventional processes.

Author Contributions

Conceptualization, H.S., E.C., H.S.G., H.S.A., P.S. and S.S.; methodology, H.S., E.C., H.S.G., H.S.A., P.S. and S.S.; software, P.S., S.S. and H.S.; validation, H.S., P.S., S.S., E.C., H.S.G. and A.K.; formal analysis, P.S., S.S., H.S. and E.C.; investigation, P.S. and S.S.; resources, H.S., E.C. and A.K.; data curation, P.S. and S.S.; writing—original draft preparation, P.S. and S.S.; writing—review and editing, H.S., E.C., H.S.G., P.S. and S.S.; visualization, H.S., E.C., H.S.G., H.S.A., A.K., P.S. and S.S.; supervision, H.S., E.C., H.S.G., H.S.A. and A.K.; project administration, H.S., E.C., H.S.A. and H.S.G.; funding acquisition, H.S., E.C., H.S.G. and H.S.A. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Tables

Generate image description

Figure 1. Schematics of the pre-/post-heat treatment operations: substrate heating (SH) (up) and hot isostatic pressing (HIP) (down).

Generate image description

Figure 1. Schematics of the pre-/post-heat treatment operations: substrate heating (SH) (up) and hot isostatic pressing (HIP) (down).

Generate image description

Figure 2. Experimental flowchart of the entire study.

Generate image description

Figure 3. SEM micrographs of as-received Ni–20Cr powder feedstock used for cold spray additive manufacturing at (a) lower and (b) higher magnification.

Generate image description

Figure 4. EDS spectrum of as-received Ni–20Cr powder feedstock.

Generate image description

Figure 5. XRD data of as-received Ni–20Cr powder feedstock and cold spray additive manufactured Ni–20Cr thick plates along with a magnified view.

Generate image description

Figure 6. Macrographs of the cold spray additive manufactured Ni–20Cr thick plates: (a) As-sprayed; (b) Substrate heated; (c) Hot-isostatic pressing treated.

Generate image description

Figure 7. Cross-sectional SEM analysis of the cold spray additive manufactured Ni–20Cr thick plates: (a) As-sprayed; (b) Substrate heated; (c) Hot-isostatic pressing treated, pores in the microstructures are encircled.

Generate image description

Figure 8. Density, apparent surface porosity, and pore size data of the cold spray additive manufactured Ni–20Cr thick plates in as-sprayed, substrate-heated, and hot-isostatic pressing treated conditions.

Generate image description

Figure 9. EDS spectra of the cold spray additive manufactured Ni–20Cr thick plates: (a) As-sprayed; (b) Substrate heated; (c) Hot-isostatic pressing treated.

Generate image description

Figure 10. Combined load-displacement nanoindentation curves for the cold spray additive manufactured Ni–20Cr thick plates in as-sprayed, substrate heated, and hot-isostatic pressing treated conditions.

Generate image description

Figure 11. Engineering stress vs engineering strain curves for the cold spray additive manufactured Ni–20Cr thick plates in as-sprayed, substrate heated, and hot-isostatic pressing treated conditions.

Generate image description

Figure 12. Plot of weight loss/area vs. number of cycles for the cold spray additive manufactured Ni–20Cr thick plate in substrate heated condition (Ni–20Cr-SH) exposed to 50 cycles of high-temperature cyclic oxidation in air at 900 °C.

Generate image description

Figure 13. Plot of (weight loss/area)2 vs. number of cycles for the cold spray additive manufactured Ni–20Cr thick plate in substrate heated condition (Ni–20Cr-SH) exposed to 50 cycles of high-temperature cyclic oxidation in air at 900 °C.

Generate image description

Figure 14. Macrographs of the cold spray additive manufactured Ni–20Cr thick plate in substrate-heated condition (Ni–20Cr-SH) exposed to 50 cycles of high-temperature cyclic oxidation in air at 900 °C.

Generate image description

Figure 15. Surface SEM image of oxide scale for the cold spray additive manufactured Ni–20Cr thick plate in substrate-heated condition (Ni–20Cr-SH) subjected to 50 cycles of high-temperature cyclic oxidation in air at 900 °C.

Generate image description

Figure 16. EDS analysis of oxide scale for the cold spray additive manufactured Ni–20Cr thick plate in substrate-heated condition (Ni–20Cr-SH) subjected to 50 cycles of high-temperature cyclic oxidation in air at 900 °C.

Generate image description

Figure 17. XRD analysis of oxide scale for the cold spray additive manufactured Ni–20Cr thick plate in substrate-heated condition (Ni–20Cr-SH) subjected to 50 cycles of high-temperature cyclic oxidation in air at 900 °C.

Table 1

Detail of cold spraying process parameters and pre- and post-heat treatment.

Cold Spraying Parameters
Gas Used Gun Chamber Pressure Gun Chamber Temperature Standoff Distance	Nitrogen40 bar550 °C30 mm
Pre- and Post-Heat Treatment Details
Substrate Heating (SH)
Temperature of the substrateMedium Used	524 °COxy-fuel torch
Hot Isostatic Pressing (HIP)
TemperaturePressureTime Duration	900 °C104 N/mm22 h

Table 2

Details of cold spray additively manufactured Ni–20Cr samples.

Powder Material	Mandrel Material	Powder Size	Pre-/Post-Treatment	Layer Thickness	Sample ID
Ni–20Cr	IN718	5–45 µm	As Sprayed	06 mm	Ni–20Cr-AS
Ni–20Cr	IN718	5–45 µm	Hot Isostatic Pressing	10 mm	Ni–20Cr-HIP
Ni–20Cr	IN718	5–45 µm	Substrate Heating	06 mm	Ni–20Cr-SH

Table 3

Microhardness, nanohardness, and elastic modulus data of the cold spray additive manufactured Ni–20Cr thick plates in as-sprayed, substrate heated, and hot-isostatic pressing treated conditions.

Name of Sample	Microhardness (HV)	Nanohardness (GPa)	Modulus of Elasticity (GPa)
Ni–20Cr-AS	389 ± 50	6.8 ± 0.7	229 ± 11
Ni–20Cr-SH	422 ± 10	6.3 ± 0.4	210 ± 7
Ni–20Cr-HIP	185 ± 15	4.8 ± 0.5	227 ± 9

Table 4

Comparison of macro tensile data of the cold spray additive manufactured Ni–20Cr thick plates in as-sprayed, substrate heated, and hot-isostatic pressing treated conditions with that of bulk Ni–20Cr alloy [24].

Mechanical Property	Bulk Material	Ni–20Cr-AS	Ni–20Cr-SH	Ni–20Cr-HIP
Modulus of elasticity, GPa	214	111 ± 19	200 ± 15	142 ± 17
Ultimate tensile strength, MPa	730	590 ± 29	635 ± 20	512 ± 23
Yield strength, MPa	350	270 ± 19	301 ± 13	260 ± 14
% age elongation (%)	28	7.1 ± 1.5	10.5 ± 1.1	28 ± 1.0

References

1. Bala, N.; Singh, H.; Prakash, S. Characterization and High-Temperature Oxidation Behavior of Cold-Sprayed Ni-20Cr and Ni-50Cr Coatings on Boiler Steels. Metall. Mater. Trans. A; 2011; 42, pp. 3399-3416. [DOI: https://dx.doi.org/10.1007/s11661-011-0759-z]

2. Zhou, C.H.; Zhang, H.; Guan, X.G.; Pan, R.Y.; Sun, F.J.; Mao, N.N. High Temperature Oxidation of Ni-20Cr Alloy under Compressive Stress. IOP Conf. Ser. Earth Environ. Sci.; 2019; 233, 032005. [DOI: https://dx.doi.org/10.1088/1755-1315/233/3/032005]

3. Lund, R.W.; Nix, W.D. High Temperature Creep of Ni-20Cr-2ThO2 Single Crystals. Acta Metall.; 1976; 24, pp. 469-481. [DOI: https://dx.doi.org/10.1016/0001-6160(76)90068-7]

4. Tharajak, J.; Sanpo, N. The Study on High Temperature Stability Test of Ni/Cr Cold Spray Coating. Appl. Mech. Mater.; 2020; 901, pp. 43-48. [DOI: https://dx.doi.org/10.4028/www.scientific.net/AMM.901.43]

5. Kumar, M.; Singh, H.; Singh, N. Study of Ni-20Cr Coatings for High Temperature Applications-A Review. Arch. Metall. Mater.; 2013; 58, pp. 523-528. [DOI: https://dx.doi.org/10.2478/amm-2013-0030]

6. Belitskii, M.E. A Method of Manufacture and Some Properties of Sintered 20Cr-80Ni Nichrome. Sov. Powder Metall. Met. Ceram.; 1965; 4, pp. 741-745. [DOI: https://dx.doi.org/10.1007/BF00774223]

7. Kruth, J.-P.; Leu, M.C.; Nakagawa, T. Progress in Additive Manufacturing and Rapid Prototyping. CIRP Ann.; 1998; 47, pp. 525-540. [DOI: https://dx.doi.org/10.1016/S0007-8506(07)63240-5]

8. Gibson, I.; Rosen, D.W.; Stucker, B. Additive Manufacturing Technologies: 3D Printing, Rapid Prototyping and Direct Digital Manufacturing; 2nd ed. Springer: New York, NY, USA, London, UK, 2015.

9. Murr, L.E.; Gaytan, S.M.; Ramirez, D.A.; Martinez, E.; Hernandez, J.; Amato, K.N.; Shindo, P.W.; Medina, F.R.; Wicker, R.B. Metal Fabrication by Additive Manufacturing Using Laser and Electron Beam Melting Technologies. J. Mater. Sci. Technol.; 2012; 28, pp. 1-14. [DOI: https://dx.doi.org/10.1016/S1005-0302(12)60016-4]

10. Bartkowiak, K.; Ullrich, S.; Frick, T.; Schmidt, M. New Developments of Laser Processing Aluminium Alloys via Additive Manufacturing Technique. Phys. Procedia; 2011; 12, pp. 393-401. [DOI: https://dx.doi.org/10.1016/j.phpro.2011.03.050]

11. Kruth, J.-P.; Levy, G.; Klocke, F.; Childs, T.H.C. Consolidation Phenomena in Laser and Powder-Bed Based Layered Manufacturing. CIRP Ann.; 2007; 56, pp. 730-759. [DOI: https://dx.doi.org/10.1016/j.cirp.2007.10.004]

12. Pawlowski, L. The Science and Engineering of Thermal Spray Coatings; 1st ed. Wiley: Hoboken, NJ, USA, 2008; [DOI: https://dx.doi.org/10.1002/9780470754085]

13. Kaushal, G.; Singh, H.; Prakash, S. Comparative High Temperature Analysis of HVOF-Sprayed and Detonation Gun Sprayed Ni–20Cr Coating in Laboratory and Actual Boiler Environments. Oxid. Met.; 2011; 76, pp. 169-191. [DOI: https://dx.doi.org/10.1007/s11085-011-9245-7]

14. Pattison, J.; Celotto, S.; Morgan, R.; Bray, M.; O’Neill, W. Cold Gas Dynamic Manufacturing: A Non-Thermal Approach to Freeform Fabrication. Int. J. Mach. Tools Manuf.; 2007; 47, pp. 627-634. [DOI: https://dx.doi.org/10.1016/j.ijmachtools.2006.05.001]

15. Sova, A.; Grigoriev, S.; Okunkova, A.; Smurov, I. Potential of Cold Gas Dynamic Spray as Additive Manufacturing Technology. Int. J. Adv. Manuf. Technol.; 2013; 69, pp. 2269-2278. [DOI: https://dx.doi.org/10.1007/s00170-013-5166-8]

16. Papyrin, A. The Development of the Cold Spray Process. The Cold Spray Materials Deposition Process; Elsevier: Amsterdam, The Netherlands, 2007; pp. 11-42. [DOI: https://dx.doi.org/10.1533/9781845693787.1.11]

17. Assadi, H.; Gärtner, F.; Stoltenhoff, T.; Kreye, H. Bonding Mechanism in Cold Gas Spraying. Acta Mater.; 2003; 51, pp. 4379-4394. [DOI: https://dx.doi.org/10.1016/S1359-6454(03)00274-X]

18. Vargas-Uscategui, A.; King, P.C.; Yang, S.; Chu, C.; Li, J. Toolpath Planning for Cold Spray Additively Manufactured Titanium Walls and Corners: Effect on Geometry and Porosity. J. Mater. Process. Technol.; 2021; 298, 117272. [DOI: https://dx.doi.org/10.1016/j.jmatprotec.2021.117272]

19. Brodmann, F.J. Cold Spray Process Parameters: Powders. The Cold Spray Materials Deposition Process; Elsevier: Amsterdam, The Netherlands, 2007; pp. 105-116. [DOI: https://dx.doi.org/10.1533/9781845693787.2.105]

20. Oliver, W.C.; Pharr, G.M. An Improved Technique for Determining Hardness and Elastic Modulus Using Load and Displacement Sensing Indentation Experiments. J. Mater. Res.; 1992; 7, pp. 1564-1583. [DOI: https://dx.doi.org/10.1557/JMR.1992.1564]

21. Mazhdi, M.; Tafreshi, M.J. The Effects of Gadolinium Doping on the Structural, Morphological, Optical, and Photoluminescence Properties of Zinc Oxide Nanoparticles Prepared by Co-Precipitation Method. Appl. Phys. A; 2018; 124, 863. [DOI: https://dx.doi.org/10.1007/s00339-018-2291-0]

22. Marzbanrad, B.; Jahed, H.; Toyserkani, E. On the Evolution of Substrate’s Residual Stress during Cold Spray Process: A Parametric Study. Mater. Des.; 2018; 138, pp. 90-102. [DOI: https://dx.doi.org/10.1016/j.matdes.2017.10.062]

23. Li, Y.; Dong, T.; Fu, B.; Li, G.; Liu, Q. Study of the Microstructure and Properties of Cold Sprayed NiCr Coating. J. Mater. Eng. Perform.; 2021; 30, pp. 9067-9077. [DOI: https://dx.doi.org/10.1007/s11665-021-06075-7]

24. Bobbio, L.D.; Bocklund, B.; Liu, Z.-K.; Beese, A.M. Tensile Behavior of Stainless Steel 304L to Ni-20Cr Functionally Graded Material: Experimental Characterization and Computational Simulations. Materialia; 2021; 18, 101151. [DOI: https://dx.doi.org/10.1016/j.mtla.2021.101151]

25. Chen, C.; Xie, Y.; Yan, X.; Yin, S.; Fukanuma, H.; Huang, R.; Zhao, R.; Wang, J.; Ren, Z.; Liu, M. et al. Effect of Hot Isostatic Pressing (HIP) on Microstructure and Mechanical Properties of Ti6Al4V Alloy Fabricated by Cold Spray Additive Manufacturing. Addit. Manuf.; 2019; 27, pp. 595-605. [DOI: https://dx.doi.org/10.1016/j.addma.2019.03.028]

26. Annasamy, M.; Haghdadi, N.; Taylor, A.; Hodgson, P.; Fabijanic, D. Static Recrystallization and Grain Growth Behaviour of Al0.3CoCrFeNi High Entropy Alloy. Mater. Sci. Eng. A; 2019; 754, pp. 282-294. [DOI: https://dx.doi.org/10.1016/j.msea.2019.03.088]

27. Cinca, N.; Drehmann, R.; Dietrich, D.; Gärtner, F.; Klassen, T.; Lampke, T.; Guilemany, J.M. Mechanically Induced Grain Refinement, Recovery and Recrystallization of Cold-Sprayed Iron Aluminide Coatings. Surf. Coat. Technol.; 2019; 380, 125069. [DOI: https://dx.doi.org/10.1016/j.surfcoat.2019.125069]

28. Zheng, L.; Schmitz, G.; Meng, Y.; Chellali, R.; Schlesiger, R. Mechanism of Intermediate Temperature Embrittlement of Ni and Ni-Based Superalloys. Crit. Rev. Solid State Mater. Sci.; 2012; 37, pp. 181-214. [DOI: https://dx.doi.org/10.1080/10408436.2011.613492]

29. Samaee, V.; Sandfeld, S.; Idrissi, H.; Groten, J.; Pardoen, T.; Schwaiger, R.; Schryvers, D. Dislocation Structures and the Role of Grain Boundaries in Cyclically Deformed Ni Micropillars. Mater. Sci. Eng. A; 2020; 769, 138295. [DOI: https://dx.doi.org/10.1016/j.msea.2019.138295]

30. Hay, J.C.; Pharr, G.M. Experimental Investigations of the Sneddon Solution and an Improved Solution for the Analysis of Nanoindentation Data. MRS Proc.; 1998; 522, 39. [DOI: https://dx.doi.org/10.1557/PROC-522-39]

31. Hosford, W.F.; Caddell, R.M. Metal Forming: Mechanics and Metallurgy; 3rd ed. Cambridge University Press: New York, NY, USA, 2007.

32. Hay, J.C.; Bolshakov, A.; Pharr, G.M. A Critical Examination of the Fundamental Relations Used in the Analysis of Nanoindentation Data. J. Mater. Res.; 1999; 14, pp. 2296-2305. [DOI: https://dx.doi.org/10.1557/JMR.1999.0306]

33. King, R.B. Elastic Analysis of Some Punch Problems for a Layered Medium. Int. J. Solids Struct.; 1987; 23, pp. 1657-1664. [DOI: https://dx.doi.org/10.1016/0020-7683(87)90116-8]

34. Berthod, P. Kinetics of High Temperature Oxidation and Chromia Volatilization for a Binary Ni–Cr Alloy. Oxid. Met.; 2005; 64, pp. 235-252. [DOI: https://dx.doi.org/10.1007/s11085-005-6562-8]

35. Watanabe, T.; Ikeda, K.; Katayama, M.; Inada, Y. In-Situ XAFS Study for Calcination Process of Cr Catalyst Supported on γ-Al₂ O₃ and SiO₂. J. Phys. Conf. Ser.; 2016; 712, 012073. [DOI: https://dx.doi.org/10.1088/1742-6596/712/1/012073]