Effect of SMRT on Microstructure and Mechanical Properties of Zr-4 Alloy

The microstructure and mechanical properties of as-annealed Zr-4 alloy subjected to surface mechanical rolling treatment (SMRT) were investigated. The effect of rolling passes and rolling depth per pass on the thicknesses of NG (nano grain)/UFG (ultrafine grain) layer and deformed layer in the SMRTed Zr-4 alloy were studied. The optimized process parameters are 8 passes and depth of 40 μm per pass. A gradient microstructure consisting of a NG/UFG layer of 100 μm in thickness, a deformed layer of 300 μm in thicknesses and a CG (coarse grain) layer are produced in the SMRTed Zr-4 alloy from the treated surface to the matrix. The microhardness on surface significantly increases due to SMRT. The yield stress and ultimate tensile strength of SMRTed Zr-4 alloy are 352 and 600 MPa, increased by 7% and 9%, respectively. And the elongation is slightly reduced. The yield strength 362 MPa calculated by the rule-of-mixture is similar to the experimental value.