Preparation of graded multilayer materials and evaluation of residual stresses

It is generally difficult to join ceramics to alloys by conventional welding technologies to fabricate graded multilayer materials with various excellent engineering properties. In this study, MoSi2 and 316L stainless steel are chosen a typical example and are joined together using the spark plasma sintering technique. To evaluate the joint quality, the interlayer system of the graded material is characterized using analysis of the residual stress by the finite element ANSYS code. The results show that dense uniformed joints can be achieved with such graded inter-layers because the coefficient of thermal expansion (CTE) of each interlayer closely matched over a wide temperature range. Such a compatibility between the graded inter-layers prevents MoSi2 with low toughness from the occurrence of microcracks resulted from the residual stresses formed during cooling of the joint. Further theoretical analysis indicates that with the increase in the compositional distribution exponent (P), maximum radial and axial residual tensile stress first increases and then decreases. In addition, with the increase in the number (n) of graded layer, maximum radial and axial residual tensile stress decreases gradually.