Effect of Minor Boron Addition on the Fatigue Strength and High Temperature Properties of Injection Molded Ti-6Al-4V Compacts

Abstract

Ti-6Al-4V alloy has attracted a lot of attention from the automotive and aerospace industries because of their outstanding specific strength and corrosion resistance. On the other hand, Ti-6Al-4V alloy has normally poor workability because of the low thermal conductivity and the low elastic modulus. Metal injection molding (MIM) process is expected to manufacture a complex part with near net shape and reduce the manufacturing cost. However, Ti-6Al-4V alloy compacts by MIM process had a problem of low fatigue strength compared to wrought material.In this study, we tried to add a minor amount of boron using TiB 2 powder for improving the fatigue strength. Addition of boron resulted refinement of the grain size of lamellar structure, which lead to increase the high cycle fatigue strength and fatigue limit. In addition, tensile properties at high temperature was investigated. KEY WORDSmetal injection molding, Ti-6Al-4V, fatigue strength, high temperature strength, titanium boride

Effect of α + β region sintering on the mechanical properties of injection molded Ti-6Al-4V compacts

“…13 Relationships between ratio of estimated value of maximum pore diameter to mean grain diameter and ratio of fatigue strength based on HIP treated compacts. Data of boron added compacts and Ti64-fine powder compacts are references (Choe et al, 2016) .…”

“…Several papers have reported that the fatigue strength of the Ti-6Al-4V alloy is proportional to the reciprocal of the square root of the grain size (Choe et al, 2016) (Okazaki et al, 1992) . This means that the fatigue strength and the fatigue crack initiation stress are equal.…”

“…This result showed that the crack initiation stress (equivalent to the fatigue strength in Ti alloy) decreases as the ratio of the inclusion diameter and the slip band length (corresponding to the grain size) to the grain boundary increases. Therefore, it is thought that the influence of relative magnitude relationship between the pore diameter and the grain diameter on the fatigue strength can be evaluated by the "the ratio of fatigue added compacts and Ti64-fine powder compacts are references (Choe et al, 2016) .…”

Metal injection moulding of titanium and titanium alloys: Challenges and recent development

“…Nonetheless, research has demonstrated that it is possible for the MIM process to manufacture Ti64 components with superior mechanical properties close to the ASTM standard range [5,43,51,100,101] especially by small addition of other elements such as B [43,45], C [71], Gd [58] and TiC [81]. However, most research work on MIM of Ti64 alloy has been specifically designed for biomedical applications [43,83,102] rather than other applications such as aerospace. Table 1, summarizes powder and binder characteristics as well as properties obtained from some selected research on MIM of Ti64 alloys.…”

“…The most successful process may be a small addition of grain refining agents such as boron, LaB 6 and TiC to the feedstock [43,45,[81][82][83]. Post sintering heat treatments may also improve the ductility and strength of MIM components through their modification of microstructure.…”