Time-dependent twinning during ambient temperature compression creep of alpha Ti-0.4Mn alloy

Abstract

The experimental observations of Kulkarni and Hong haveCreep of Alpha Ti-0.4Mn Alloy a simple explanation that does not involve superheating behavior in NiAl. Similar time-temperature profile observa-CARL A. HULTGREN, CHARLES A. GREENE, and tions have been made in our laboratory on these alloys SREERAMAMURTHY ANKEM in electromagnetic levitation processing. We attribute this behavior to the formation of a surface oxide layer on solidi-Titanium alloys find applications in a wide variety of technological fields including aerospace, marine, chemical, fied samples. This surface oxide has a much higher emissivsporting goods, power generation, and biomedical. In many ity that the clean solid or the liquid melt, so that the apparent of these applications, the titanium alloys are subjected to temperature on reheating of the solid is much higher than the stresses over extended periods of time. In this regard, Ankem apparent temperature of the liquid at the melting temperature. et al. [1] have shown that the titanium plus 0.4 wt pct manga-The apparent reduction in temperature on melting, shown nese alloy (Ti-0.4Mn) with 0.071 wt pct oxygen creeps at in the authors' Figure 2, is simply the melting or dissolution ambient temperature when subjected to 95 pct of its 0.2 pct of this surface oxide to reveal the liquid at the melting yield stress. They [1] have found that time-dependent twinning temperature.is a predominant mechanism. The aim of this investigation We have processed NiAl alloys in a vacuum of 1 ϫ 10 Ϫ5 is to study whether this alloy also creeps in compression, torr for as long as 20 minutes at apparent temperatures whether twinning is a deformation mechanism, and whether several hundred degrees above the melting temperature in the twinning mode is different from that observed earlier [1] an effort to dissolve this oxide layer. Following one of these in tension. experiments, the sample was cooled and removed from the The compression specimens were 0.25-in. square and chamber, and a deep groove was cut in the sample with a 0.50-in. long, machined from the heads of the previously mill bastard file. The sample was reinserted into the chamber tested [1] tensile specimens [2,3] with original head root diameand was melted at the normal apparent melting temperature ter of 0.425 in., while the diameter in the region of the gage during heating. Filing the oxide layer allows liquid from the length was less than 0.25 in. Hence, no plastic deformation is interior to flow over the surface of the sample and dissolve expected to have occurred in the head region during previous the surface oxide. High-temperature alloys containing alumitensile creep tests. The specimens were cut with an electron num readily form surface oxides, and these oxides are diffidischarge machine to avoid surface strain and to provide a cult to reduce. In processing Nb 3 Al alloys, it was common high-quality surface finish. The specimens were electroto reach very high apparent temperatures (Ͼ2500 K) while polished and fiducial gold grid lines were put on t...

The effects of stress level and grain size on the ambient temperature creep deformation behavior of an alpha Ti-1.6 wt pct V alloy

“…As mentioned before, [13,16,17] Ti-0.4Mn alloy, namely, fine slip along with the formation of twins. This suggests that time-dependent twinning is characteristic of near-␣ Ti alloys with a low percentage of ␤-stabilizer.…”

“…Creep strain of 0.008 was seen after a time of approximately 22 hours. Most of the recent investigations [10][11][12][13][14][15][16][17][18][19][20][21] are concerned with the determination of the deformation mechanisms of lowtemperature creep. In this regard, Ankem et al [13] have shown that time-dependent twinning is a major mechanism of ambient temperature creep in the coarse-grained ␣-Ti-0.4 wt pct Mn alloy.…”