Temperature Dependence Of Elongation Research Articles

Transformation behavior of a Ti–47Ni–3Cu alloy heat treated under temperature gradient

Transformation behavior and shape memory characteristics of temperature gradient anneal (TGA) treated and thermo-mechanically treated (TMT) Ti–47Ni–3Cu(at.%) alloys were investigated by means of differential scanning calorimetry and thermal cycling tests under constant load. Both TGA treated and TMT Ti–47Ni–3Cu alloys showed B2–B19′ transformation behavior. The change in Ms * by 23 K was developed in the TGA treated Ti–47Ni–3Cu alloy along the length of the sample (150 mm). TGA treated Ti–47Ni–3Cu alloy showed perfect shape memory effects. The temperature dependence of elongation (dε/dT) of a TGA treated specimen was in the range of 0.02–0.09% K−1 depending on the amount of applied stress, which was small compared to that of a TMT specimen (0.01–0.18% K−1). The temperature dependence of elongation (dε/dT) of the TGA treated specimen on cooling is almost the same as that on heating, while dε/dT of the TMT specimen on cooling is much smaller than that on heating (0.68% K−1).

Superplasticity of Fine-Grained Titanium Allloys Obtained through Protium Treatment.

To obtain fundamental data on superplasticity of fine-grained α+β type titanium alloys obtained through protium treatment, superplasticity tensile tests were carried out in vacuum, the strain-rate and temperature dependence of elongation and flow stress n fine-grained Ti-6Al-4V alloy were investigated. Then, changes in microstructure after the tensile test were observed using an optical and scanning electron microscope. Coarse-grained titanium alloy was also tested, and compared with fine-grained alloy. Experimental results are as follows:Fine-grained material having a grain size of 1μm to 3μm shows elongation of over 3700% at a testing temperature of 1123 K and 1173K, and a strain rate of 1×10-3S<-1>. When the maximum elongation of fine-grained material was investigated, the material showed a huge elongation of more than 8008% at a testing temperature of 1123K and a strain rate of 1×10-3S<-1>. The m-value of fine-grained material is much higher than that of coarse-grained material, with the maximum m-values being 0.80 and 0.64 respectively. These results indicate that it is not easy to occur a necking in fine-grained material. In the observation of structure after the superplasticity tensile test, coarse-grained material did not exhibit grain growth, but fine-grained material did.