Microstructural evolution and formation mechanism of FCC titanium hydride in Ti–6Al–4V–xH alloys

Influence of hydrogen content on tensile and compressive properties of Ti–6Al–4V alloy at room temperature

“…Orthorhombic ␣ martensite forms more easily in alpha and beta type titanium alloys with a large amount of beta-stabilizing alloying elements, which has been reported previously by Qazi et al [14], Fang and Wang [4] and Niinomi et al [15]. Some diffraction peaks of ␣ phase become wider because of the overlap of ␣ phase and ␦ phase peaks and the distortion of ␣ phase lattice [16,17]. The peaks shift to the lower angles because of the expansion of crystal lattice around the interstitial hydrogen atoms owing to the solution of hydrogen atoms [15,17].…”

“…Some diffraction peaks of ␣ phase become wider because of the overlap of ␣ phase and ␦ phase peaks and the distortion of ␣ phase lattice [16,17]. The peaks shift to the lower angles because of the expansion of crystal lattice around the interstitial hydrogen atoms owing to the solution of hydrogen atoms [15,17].…”

Effect of temperature on hydrogen absorption characteristic and microstructural evolution of TC21 alloy

“…A model of eutectoid transformation has been established by Shan et al [26] and Luo et al [30] to explain the mechanism of d hydride formation in b phase according to the TieH and Tie6Ale4VeH phase diagram. However, the distinct differences between microstructures of TC21 alloy hydrogenated at 550 C and 650 C in the present work show the formation mechanisms of d hydride in TC21 alloy cannot be explained by eutectoid transformation.…”

“…The XRD patterns of the alloy hydrogenated at 550 C and 650 C are very similar but different with those at 750 C. The relative intensities of a phase in phase requires high (above 8%) aluminium concentration, which indicates that alloying with hydrogen leads to redistribution of the alloying elements [25]. Additionally, the peaks of a H phase and b H phase move to low angle, which is caused by the expansion of lattice parameter after hydrogenation [26].…”

Effect of 0.770wt%H addition on the microstructure of Ti–6Al–4V alloy and mechanism of δ hydride formation

“…A model of martensitic phase transformation has been stated by Xiao [17] to explain the mechanism of hydride formation in ␣ titanium alloys, but the hydrogen diffusion is inevitable in titanium alloys [18,19]. Lately, Luo et al [20] and Shan et al [21] used Ti-6Al-4V-H pseudo phase diagram and Ti-H phase diagram respectively, and established a model of eutectoid transformation to explain the mechanism of ␦ hydride formation. According to the Ti-6Al-4V-H pseudo phase diagram [22], the eutectoid reaction ␤ H → ␣ + ␦ can't occur in the Ti-6Al-4V alloy with 0.302 wt%H (12.14 at%H), so it is unsuitable that Luo used the model of eutectoid transformation to explain ␦ hydride formation in the alloy with 0.302 wt%H.…”