A Quantitative Study on the Effect of Heat Treatment on the Microstructure and Orientation of Titanium Hydride in Electrochemically Hydrogenated Pure Titanium

The electrochemical hydrogen charging of pure titanium and its alloys has been investigated previously, while how a subsequent annealing treatment affects the type of hydride and its orientation relationship with matrix is not clear. In the present study, a quantitative study on the microstructure and orientation of titanium hydrides during electrochemical hydrogen charging and subsequent annealing treatment was carried out using scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction. The results show that delta-hydride is the main in both the electrochemically hydrogenated sample and the subsequent annealing treated sample. After electrochemical hydrogen charging for 48 h, the surface is mainly composed of dense d-hydride with a thickness of approximately 42 mu m, the orientation relationship between a-matrix and d-hydride follows only the orientation relationship of OR2, {0001}(a)//{1 (1) over bar1}(delta), < 1 (2) over bar 10 >(delta)//< 110 >(delta) and an interface plane {10 (1) over bar3}(alpha)//{1 (1) over bar0}(delta). Besides OR2, a part of hydrides show an orientation relationship of OR1 with the matrix after annealing, {0001}(alpha)//{001}(delta), < 1 (2) over bar 10 >(alpha)//< 110 >(delta) and an interface plane of {1010} a//{110} d. It is further found that the relative frequency of OR1and OR2 is closely related to annealing duration. Under an argon atmosphere at 450 degrees C, the frequencies of OR1 and OR2 are nearly balance with an annealing time of 12 h, while OR1 becomes to be the predominant one with a relative frequency of 96.5% after annealing for 96 h. The mechanism for the evolution of orientation relationship of hydrides with annealing time was discussed.

Automated summary

A quantitative study was conducted on the microstructure and orientation of titanium hydrides during electrochemical hydrogen charging and subsequent annealing treatment. The results showed that delta-hydride is the main form, and annealing treatment resulted in a new orientation relationship between hydrides and the matrix.