Deformation and strength characteristics of Laves phases in titanium alloys

The superior reinforcement nature of Laves phases make them suitable for high-strength applications. Therefore, investigations on the deformation and strength characteristics of Laves phases are useful in development of an improved Laves phase-reinforced alloy. In this work, the Vickers micro-indentation method is used to evaluate and compare the deformation and strength characteristics of a hexagonal close-packed Laves phase (C14-type) in Ti-35Zr-5Fe-6Mn (wt%) and a face-centered cubic Laves phase (C15-type) in Ti-33Zr-7Fe-4Cr (wt%), considering the same volume fraction of Laves phase (~7.0%) in these alloys. Moreover, the effects of higher volume fraction of Laves phase (19.4%) on indentation-based deformation features are evaluated in Ti-35Zr-5Fe-8Mn (wt%). Remarkably, dislocation activity and plastic deformation features are evident in the C15-type Laves phase, whereas the C14-type Laves phase strongly blocks dislocation motion. Therefore, the C15-type Laves phase improves plastic deformability, whereas the C14-type Laves phase improves strength characteristics of Laves phase-reinforced alloys

Beta-type Ti-Nb-Zr-Cr alloys with large plasticity and significant strain hardening

A series of Ti-25Nb-8Zr-xCr (x = 0, 2, 4, 6, 8 wt%) alloys were designed based on DV-Xα cluster method and e=a-Δr diagram with an anticipation to obtain high plasticity and significant strain hardening. The designed alloys were produced through cold crucible levitation melting technique in order to effectively investigate their micro-structures and mechanical properties. The addition of Cr significantly enhances the β stability in the microstructures of the Ti-25Nb-8Zr-xCr alloys. Both yield strength and hardness of the studied alloys increase due to the effect of solid-solution strengthening. By contrast, the plasticity, maximum strength and strain hardening rate are influenced by theβstability as well as the distinct deformation mechanisms. None of the alloys comprising Cr fail up to 100 kN (the load capacity used) and all show impressive plasticity (~75%) and superior maximum compressive strength (~4.5 GPa) at 100 kN. Moreover, the deformation bands, which are found around the hardness indentations, are analyzed for all the investigated alloys. The fracture behaviors of the Ti-25Nb-8Zr-xCr alloys are also studied to observe the characteristics related to crack propagation, plastic deformation and the formation of shear bands

Improved deformation behavior in Ti-Zr-Fe-Mn alloys comprising the C14 type Laves and β phases

Laves phase alloys are promising materials for several structural applications, but the extreme brittleness is the predominant shortcoming of a Laves matrix. One potential solution to overcome this shortcoming is to alloy Laves matrix with some soft matrix. A group of Ti-35Zr-5Fe-xMn (x = 0, 2, 4, 6, 8 wt%) alloys was cast with an aim to improve deformation in Laves alloy compositions. The phase and microstructure analyses reveal dual phase matrices, including a β phase and a C14 type Laves phase in the investigated alloys. The mechanical properties such as yield strength, hardness and plastic strain for the investigated alloys are found to be significantly sensitive to volume fraction of the Laves phase. Ti-35Zr-5Fe shows impressive ultimate compressive strength (~1.7 GPa), yield strength (1138 MPa) and large plastic strain (23.2 %). The fracture mechanisms are dependent on the microstructure of the alloys. Additionally, the work-hardening ability of the investigated alloys have also been evaluated based on the analyses of slip band patterns formed around the micro-hardness indentations. Notably, the extreme brittleness is not encountered in all the Ti-35Zr-5Fe-xMn alloys and all exhibit very good compressive elongation including the maximum (32.5 %) in Ti-35Zr-5Fe