Experimental Analysis of Heat Treatment Effects on Microstructure, Mechanical Properties, and Fracture Behavior of NiCr20TiAl Alloy

Abstract

NiCr20TiAl is a nickel based superalloy widely used in high temperature applications such as engine valves and turbine blades, where resistance to chemical attack and thermal degradation is critical. This study presents an experimental investigation into the relationship between heat treatment, microstructure, mechanical properties and fracture behavior of NiCr20TiAl. Samples were subjected to various heat treatment regimes, followed by microstructural characterization using optical microscopy, hardness and tensile testing at both room and elevated temperatures. Fractographic analysis was conducted using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) to identify fracture mechanisms and the role of precipitates in fracture initiation. Results show that fine grains with annealing twins were observed up to a solution annealing temperature of 1080°C, beyond which grain coarsening occurred. Aging promoted significant precipitation along grain boundaries with negligible grain growth. The optimal mechanical properties were observed for the T4 (1040°C solution annealed) and T11conditions, with T11 (1040°C solution annealed and aged) exhibiting the highest tensile strength (1283 MPa) and hardness (368 HV), albeit with slightly reduced ductility. Hardness improved by aging around 80%, with a maximum value observed for T11 as 368 HV. At elevated temperatures, aged samples maintained superior properties up to 700°C, beyond which performance declined. The optimized heat treatment of 1040°C solution annealing and aging at 700°C proved most suitable for high temperature applications below 700°C.