Continuous cooling β-to-α transformation behaviors of extra-pure and commercially pure Ti

Abstract

The in-situ continuous cooling ␤-to-␣ transformation kinetics of extra-pure (EP) Ti and of grade-4 commercially pure (CP) Ti were investigated using a fully computer-controlled resistivity-temperature realtime measurement apparatus and transmission electron microscopy. The ␤-to-␣Ј martensitic transformation occurs under near pure shear condition, and the habit plane of lath-type martensite was determined to be parallel to , which is in good agreement with the prediction of the crystallographic theory. The M s temperature of EP-Ti was measured as 800 °C and can be raised by up to about 40 °C due to the generation of thermal stress and local deformation during rapid cooling. The massive transformation was, for the first time, observed to occur over a wide range of cooling rates in an EP-Ti. The massive start temperature and its occurrence were, unlike the martensitic transformation, hardly affected by the generation of thermal stress and local deformation during rapid cooling. The stable regime of massive transformation in a grade-4 CP-Ti was considerably shifted toward a slower cooling rate side and was significantly contracted at the same time. This is because the presence of iron impurity not only largely suppresses the massive transformation but also significantly delays a long-range diffusional transformation. 54336b(4150)a¿

Preparation of weak-textured commercially pure titanium by electron beam melting

“…The martensite start temperature (M S ) of CP-Ti is as high as 850 °C [34], rather higher than the preheating temperature (650 °C in this case), and the preheating temperature roughly corresponds to the surface temperature of powder bed where melting of powder occurs [35]) as well as to the post-solidification sample temperature. In addition, the cooling rate just after the powder melting stage in the EBM fabrication can be assumed to be between 10 3 −10 5 K s −1 [30].…”

Microstructural aspects of laser surface treatment of commercially pure titanium

“…The morphology and degree of martensite refinement depend on the material cooling rate [21]. The lathtype martensite is reported to occur for cooling rates above 10 3 K s −1 [22], while even higher rates of cooling (10 5 -10 6 K s −1 ) may produce a finer lath-type α martensite or a fine acicular martensitic morphology [23]. In all the analysed samples the acicular martensitic phase was dominant.…”

Residual oxygen content and powder recycling: effects on microstructure and mechanical properties of additively manufactured Ti-6Al-4V parts

“…12 Contour plot of ultimate tensile strength (a) and elongation (b) depending on the factors scanning speed, laser power, and hatch spacing; the colors indicate the response values from low (red) to high (green); maximum and minimum values are marked melt pool [17]. Metastable acicular '-martensite forms in the prior -grains by a diffusionless, shear-type transformation for cooling rates above 10 3 K/s [46,47]. The martensite needles are oriented about 40° to the building direction (BD) [48] due to the Burgers relation between / '-phase and -phase [49] given in Eqs.…”