Compression And Fatigue Behavior Of Gradient Porous Ti-15Mo Alloy

The treatment of large bone defects has been an important challenge in plastic surgery.Scaffold-based bone tissue engineering offers a promising future for the treatment of bony defects.The structure of natural bone(especially long bone)gradually changes from cortical outer bone to trabecular inner bone,which leads to a gradual decrease in mechanical strength of long bone from outer to inner.Therefore,the gradient porous structure of titanium alloy,which is in line with the characteristics of biological materials,can be better adapted to the characteristics of human bone as a bone implant,and is an effective solution to the "stress shielding" effect and biocompatibility of bone implants.In this paper,the effects of porosity,pore size and gradient on the compressive mechanical properties and fatigue behavior of the gradient porous Ti-15Mo alloy prepared by lateral loading selective laser melting are systematically investigated to analyze the deformation failure mechanism during compression and reveal the mechanism of fatigue damage.The main findings are as follows:(1)By means of gradient porous Ti-15Mo alloy specimens with pore diameters of 7.87 mm、3.75 mm、1.90 mm、porosities of 88.15%、90.04%、93.02%,2-fold gradient,3-fold gradient and 4-fold gradient at a strain rate of 0.2 s-1,it was found that the compression deformation process of laterally loaded gradient porous Ti-15Mo alloy was divided into a linear elastic stage,a densification stage and a fluctuating stage in which the number of peaks is determined according to the number of designed gradient layers,with no obvious plateau stage.(2)The elastic modulus of the specimens increases with the increase of pore diameter and decreases with the increase of porosity and gradient;their yield strength decreases with the increase of pore diameter,porosity and gradient;the compression strength decreases with the increase of pore diameter,porosity and gradient;the loading mode has a significant effect on the gradient porous Ti-15Mo alloy,and the elastic modulus,yield strength and compression strength of the specimens loaded in the forward direction are higher than those of the specimens loaded in the lateral direction.The relationship between porosity and elastic modulus,yield strength and compressive strength is exponentially confirmed that the deformation mode of gradient porous Ti-15Mo alloy is mainly a combination of tensile-bending deformation.(3)The deformation mode of the gradient porous Ti-15Mo alloy is the combination of tensile bending deformation to C-shape of the strut symmetrically layer by layer,which is caused by the stress dispersion caused by the spherical structure at the node and the improvement of stability at the node and the force situation of the strut.(4)For the gradient porous Ti-15Mo alloy,the smaller the pore size,the lower the porosity and the smaller the gradient multiplier,the longer the corresponding fatigue life of the specimen,which has certain significance for the design of gradient porous titanium alloy;the fatigue damage mechanism of gradient porous Ti-15Mo alloy is that under the action of cyclic alternating stress,the cyclic strain of the specimen accumulates,and the highest stress location such as the branch rod occurs As the crack spreads,the crack intersects with the dislocation of the screw type to form a deconstruction step,and the deconstruction step forms numerous shapes of patterns with local plastic deformation,and then the effective section of the specimen is reduced due to the expansion of the crack.Once the stress increases to the permissible stress of the material and the crack expands to the critical crack size of the material,instantaneous fracture will occur.