Research On The LBW Weldability Of Ti And Finite Element Simulation For Stresses Of Joints

Ti is dental prosthetic materials, which owns excellent comprehensive mechanical properties, good biocompatibilities and corrosion resistance. As laser beam welding (LBW) possesses energy concentration, good shaping for weld, faster heating speed and smaller HAZ, it becomes important method of welding on Ti. But because of high local heating, heat input of high power density centralized near weld beam and higher temperature grads of weldment inner due to strong temperature changes in weld zone, residual stress is produced. Therefore research on LBW technology and residual stress of joints has very important practical significance on clinical application of Ti in stomatology.Research on LBW technology shows that laser power density can be as comprehensive parameter, and the spot diameter has greater influence on joint strength than that of laser power. As laser power density increases, the strength of joins will be increased first and decreased later. It indicates that strength of joins will be better, when laser power is 1.6 kW, spot diameter is 0.7mm. Through SEM observation there are large and deep dimples in fracture region with obvious characteristics of toughness fracture. Inclusion, gas holes and micro-crack can not be found in the welded joint. Further analysis of TEM indicates that substructures of acicular martensite are composed of cellular substructure and microtwinning. It is feasible that dental Ti is welded by LBW. If proper welding technology and parameters are taken, dental Ti will own better LBW weldability.Simulation results of residual stress field in weld central cross-section show that residual stress of weldment surface is tensile stresses in X-direction and Y-direction, and residual stress of internal weldment is compressive stress from analysis on 3D dental finite element model. Residual stress of cross-section is so smaller that it won't be impacted clinical application of Ti. Research on axial residual stress shows that stress is the highest tensile stresses in weld beam and fusion line, but it is compressive stress in HAZ. Axial residual stress is the characteristic of concentrated distribution and narrowness. The tensile stress in weld beam and fusion line is much higher than that in weld central cross-section, and the larger tensile stresses will reduce strengthen of the joints. The larger welding tensile stress can lead to crack, so tensile strength, stiffness, accuracy, and dimension stability of weldment will be worsened.The research results provided data support for clinical application of Ti and possess favorable guidance meaning for predicting the residual stress of joins.