Microtucture And Mechanical Proprtities Of Boron Addition Ti-V-Al Lightweight Shape Memory Alloy

In this study B was doped to improve the yield stress of Ti-V-Al shape memory alloy.X-ray diffraction?XRD?,Differential scanning calorimetry?DSC?,Room temperature Tensile test mechanical,optical microscopy,Scanning electron microscope?SEM?,Transmission electron microscope?TEM?was ued to confirm the conformation of the phase constitution,martensitic transformation temperatures,mechanical properties and shape memory effect of?Ti-13V-3Al?_100-XB_X?X=0,0.01,0.05,0.1,0.5?alloys.It is shown that?Ti-13V-3Al?_100-XB_X alloy consists of ? " phase solely,which is orthorhombic.Same as the microstructure of Ti-13V-3Al alloy,Boron's doping haven't changed the structure of matrix.when the annealing temperature is 650?,?Ti-13V-3Al?_99.9B_0.1 alloy consists of ?" phase and a little ? phase.With the increase of annealing temperature,the size of ? phase decreases and the amount of ? phase decreases too.When the content of B is lower than 0.01at%,no second phases is observed.With the increase of B content,second phases emerged.TEM shows the second phase is TiB which is orthorhombic.TiB dispersed in matrix firstly and then formed along the boundaries of grain when B content increase.when the boron is above 0.01at%,the grain size decreases with the increase of boron content.The grain size of Ti-13V-3Al alloy is about 284?m and finally decrease to about 75?m when the B content up to0.5at%.The stability of grain size improved with the increase of Boron content.The?Ti-13V-3Al?_100-XB_X alloys exhibit the typical one-step thermoelastic martensitic transformation.The Reverse transformation temperature decreased when the content of Boron less than 0.05at% and then increased with further increase of B content.when the annealing temperature is 650?,The Peak of Reverse transformation temperature is difficult to observed.The peak appeared and increased when the annealing temperature is higher.Increase of B and thermomechanical treatement also increase the stability of martensitic transfomation during thermal cycling.the mechanical properties is obviously improved by boron addition.The yield strength and the largest stress strength firstly increases and then decreases with the increase of boron content.The largest yield stress is obtained in?Ti-13V-3Al?_99.9B_0.1?711MPa?,which is 52% improved than Ti-13V-3Al alloy?468MPa?.?Ti-13V-3Al?_99.9B_0.1 also show the largest stress strength of 987 MPa while it is only711 MPa in Ti-13V-3Al,39% improved.The stress strain is increased with the increase of boron content and reach to about 20% in?Ti-13V-3Al?99.95B0.05 and?Ti-13V-3Al?_99.9B_0.1.When the annealing temperature increased,the yield strength decreased and the stress strain increased and the yield strength increased when the solid solution time is longer.The recoverable strain increased with the increasing of Boron content.?Ti-13V-3Al?_99.9B_0.1 shows the best SME property with 4% fully recoverable strain and the recovery ratio up to 83.5% when the pre-strain is 6%.The shape memory effect decreased when the annealing temperature increased.When the annealing temperature is 700?,?Ti-13V-3Al?_99.9B_0.1 shows the best shape memory ability.