Dissimilar Titanium Alloys Research Articles

Influence of Heat Treatment on Fatigue Resistance of Electron Beam Welded Dissimilar Titanium Alloy Joints

The purpose of this study was to evaluate the influence of heat treatment on the microstructural change and low cycle fatigue (LCF) resistance of an electron beam welded (EBWed) dissimilar joint between Ti-6Al-4V and Ti17 alloys. The aging with solution (STA) had a more significant effect on the microstructure and hardness than aging, compared to the as-welded joint. The post-welded joints in both aging and STA conditions were basically cyclic stable at low strain amplitudes up to 0.6%, while cyclic softening occurred at higher strain amplitudes. The fatigue life in the aging condition was slightly longer than that in the STA condition at the lower strain amplitudes. Fatigue crack initiation occurred from the specimen surface or near-surface defect, and fatigue crack propagation was characterized mainly by the fatigue striations coupled with secondary cracks in both aging and STA conditions.

Mathematic al modelling of joint temperature during linear friction welding of dissimilar Ti - 6.5Al - 3.5Mo - 1.5Zr - 0.3Si and Ti - 5Al - 2Sn - 2Zr - 4Mo - 4Cr alloys

The linear friction welding (LFW) of dissimilar titanium alloys Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (Ti11) and Ti-5Al2Sn-2Zr-4Mo-4Cr (Ti17) was studied. Combined with experimentally recorded temperature of the specimen, the thermal history of the joint during LFW was calculated based on the equation of heat conduction. The calculated temperatures are comparable to those in experiment indicating that the proposed mathematic calculation method is appropriate to use for LFW. The highest temperature of the interface was about 1280oC and the time spent above the b transus temperature being about 4.5s in Ti17 side and 3.8s in Ti11 side, respectively. The highest temperatures of the TMAZs in Ti17 and Ti11 sides are about 1100°C and 1110°C, respectively. The cooling rate is about 250°C/s and 400°C/s in the interface and TMAZs. Fine equiaxed grains are present in the WZ, and numerous elongated grains are present in the TMAZs in both sides except a small number of fine recrystallized grains.

On microstructure and mechanical properties of linear frictionwelded dissimilar Ti–6Al–4V and Ti–6·5Al–3·5Mo–1·5Zr–0·3Sijoint

Linear friction welding of dissimilar titanium alloys Ti–6Al–4V (TC4)and Ti–6·5Al–3·5Mo–1·5Zr–0·3Si (TC11)was achieved. Microstructural examination showed that the joint has a clearlyidentified weld zone and a thermomechanically affected zone on both TC4 andTC11 sides with a clearly identified weld line. In the weld zone of TC4, superfine αgrains are dispersed in the β matrix, while in that ofTC11, a few recrystallised α grains are observed alongthe β boundaries. In the thermomechanically affectedzone of TC4, both deformed and recrystallised grains exist in the same area,while that of TC11 has a deformed α+βstructure. The tensile strength of the joint is comparable to that of theparent TC4 where fracture occurs. The joint microhardness is well relatedto its microstructure.

A fatigue assessment of dissimilar titanium alloy diffusion bonds

Diffusion bonds between the dissimilar titanium alloy pairing Ti 6/4 and Ti 550 were produced from laboratory scale plate stock materials. Metallographic sections, chemical composition and micro-hardness traverses across the bond line are all presented as evidence of the form and integrity of these joints. The mechanical performance of the bonds was assessed under both monotonic tensile and low cycle fatigue loading utilising specimens which contained bonds orientated either perpendicular or inclined to the principal stress axis. In general, near Ti 6/4 parent properties were measured under both loading conditions. However, performance was occasionally influenced by the presence of bond line defects, particularly under fatigue loading.

Effect of activity differences on hydrogen migration in dissimilar titanium alloy welds

The effect of alloy composition on hydrogen activity was measured for seven titanium alloys as a means to determine the tendency for hydrogen migration within dissimilar metal welds. The alloys were: Ti-CP, Ti-3A1-2.5V, Ti-3Al-2.5V-3Zr, Ti-3Al-2Nb-lTa, Ti-6A1, Ti-6A1-4V, and Ti-6Al-2Nb-lTa-0.8Mo. Hydrogen pressure-hydrogen concentration relationships were determined for temperatures from 600 ‡C to 800 ‡C and hydrogen concentrations up to approximately 3.5 at. pct (750 wppm). Fusion welds were made between Ti-CP and Ti-CP and between Ti-CP and Ti-6A1-4V to observe directly the hydrogen redistribution in similar and dissimilar metal couples. Hydrogen activity was found to be significantly affected by alloying elements, particularly Al in solid solution. At a constant Al content and temperature, an increase in the volume fraction ofΒ reduced the activity of hydrogen in α-@#@ Β alloys. Activity was also found to be strongly affected by temperature. The effect of temperature differences on hydrogen activity was much greater than the effects resulting from alloy composition differences at a given temperature. Thus, hydrogen redistribution should be expected within similar metal couples subjected to extreme temperature gradients, such as those peculiar to fusion welding. Significant hydrogen redistribution in dissimilar alloy weldments also can be expected for many of the compositions in this study. Hydride formation stemming from these driving forces was observed in the dissimilar couple fusion welds. In addition, a basis for estimating hydrogen migration in titanium welds, based on hydrogen activity data, is described.

Effect of activity differences on hydrogen migration in dissimilar titanium alloy welds

Effect of activity differences on hydrogen migration in dissimilar titanium alloy welds

Diffusion bonding dissimilar titanium alloys — the effect of different alloying systems on the quality of bonded joints

Diffusion bonding dissimilar titanium alloys — the effect of different alloying systems on the quality of bonded joints

Effect of solute banding on transformations in dissimilar titanium alloy weldments

Effect of solute banding on transformations in dissimilar titanium alloy weldments