Failure analysis of a gripping assembly loaded at temperatures above 1000 °C

Abstract

Abstract The aim of the present work was to study the high-temperature behavior of a Ni-15Cr-18Co-4Al-3.5Mo powder-processed polycrystalline superalloy. This superalloy has been used to make the gripping assembly of a new commercial creep testing machine up to 1200 °C. The gripping assembly was exposed to a temperature of 1100 °C for 10 days at a nominal stress of 0.3 MPa and a local peak stress of 3.5 MPa. During this creep test, unacceptable creep deformation of the gripping assembly occurred. Three states of the superalloy microstructure were studied: (i) the state at receipt; (ii) the heat-treated state (annealing, 1200 °C/10 min/air); and (iii) the state following its use as a gripping assembly adapter during the creep test. Microstructural degradation resulted from exposed γ′ phase face-centered cubic Ni3Al particles that were preferentially created at the grain boundaries. Uniaxial tensile creep tests were conducted at 870 °C over a range of applied stresses from 100 to 220 MPa, and two tests were performed at 1000 °C and 1100 °C at 100 MPa and 10 MPa, respectively. A rapid drop in both the creep strength and the oxidation resistance was observed above 1000 °C. After deformation, the microstructure was investigated using advanced SEM and TEM techniques. Based on this investigation, the studied material is not recommended for use in creep testing machine gripping assemblies at temperatures above 1000 °C.