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Titanium alloys find applications in a wide variety of technological fields including aerospace, marine, chemical, sporting goods, power generation, and biomedical. In many of these applications, the titanium alloys are subjected to stresses over extended periods of time. In this regard, Ankem et al.[1] have shown that the titanium plus 0.4 wt pct manganese alloy (Ti-0.4Mn) with 0.071 wt pct oxygen creeps at ambient temperature when subjected to 95 pct of its 0.2 pct yield stress. They[1] have found that time-dependent twinning is a predominant mechanism. The aim of this investigation is to study whether this alloy also creeps in compression, whether twinning is a deformation mechanism, and whether the twinning mode is different from that observed earlier[1] in tension.
The compression specimens were 0.25-in. square and 0.50-in. long, machined from the heads of the previously tested[1] tensile specimens[2,3] with original head root diameter of 0.425 in., while the diameter in the region of the gage length was less than 0.25 in. Hence, no plastic deformation is expected to have occurred in the head region during previous tensile creep tests. The specimens were cut with an electron discharge machine to avoid surface strain and to provide a high-quality surface finish. The specimens were electropolished and fiducial gold grid lines were put on the flats by an electron resist method.[4,5]
Photomicrographs of areas of the specimens were taken before and after quasistatic compression testing at room temperature at an engineering strain rate of 3.28 X 10^sup -5^ s^sup -1^. Optical and scanning electron micrographs of the creep specimens were also taken before and after creep testing. Continuous compressive creep tests were conducted on two specimens at 95 pct yield stress (YS) at room temperature (298 K) in air. Observation of these specimens indicated slip and twinning deformation mechanisms. To systematically determine the role of twinning on the creep strain, another specimen was crept with interruptions at predetermined time intervals. These intervals corresponded to creep strains of 0.49, 0.99, 1.34, and 1.58 pct. The presence of deformation twins during creep was confirmed by examining thin foils of specimens before and after deformation in the transmission electron microscope (TEM). Samples were prepared following the method outlined by Spurling.[6] Thin sections were cut from undeformed specimens and the gage...