Creep Behavior of ZK60 Alloy and ZK60/SiCw Composite After Extrusion and Precipitation Hardening

Abstract

Creep properties of ZK60 alloy and ZK60/SiCw composite have been investigated after extrusion and precipitation hardening by accelerated creep test. Creep tests were conducted at 150 °C in the stress range of 10–120 MPa. At low stresses, the stress exponents of 1.93 and 1.75 were obtained for the unreinforced alloy and the composite, respectively. Stress exponents of the unreinforced alloy and composite sample were 5.82 and 7.07, respectively, at high stresses. The creep mechanism changed by increasing the stress from grain boundary sliding (GBS) to dislocation creep due to the fact that the average true creep activation energy changed from 55 to 95.06 kJ/mol. Based on the microstructural observations, at low stresses, the grain refinement induced by twinning caused the GBS mechanism. However, at high stresses, slip changed from basal planes to the pyramidal secondary slip system which was associated with increase in twin density. Examination of the fracture surfaces revealed that cavity nucleation in the grain corners and around the precipitates was the main reason for creep failure.