Hot salt stress corrosion cracking by silver chloride in Ti-6Al-2Sn-4Zr-6Mo

Yitong Shi,David Dye,Rebecca Sandala,Susmitha Joseph ,Edward A Saunders ,T.c Lindley

doi:10.1051/matecconf/202032104025

Abstract

Hot salt stress-corrosion cracking (HSSCC) of titanium alloys has been found in the presence of chloride and other halide salts. Here, a series of AgCl HSSCC tests on Ti-6246 were conducted using a two-point bending rig at 380-500°C to determine the boundary conditions of stress and temperature. Rapid failure occurred after 24 hours above 440 °C, whilst the trigger stress of HSSCC was determined to be 400 MPa at 380 °C. Energy dispersive X-ray during scanning transmission electron microscopy (STEM-EDX) suggested the formation of metallic silver and chlorides of active alloying elements Al, Sn and Zr. The transgranular fracture surface is expected to be linked to an underlying hydrogen embrittlement via hydrogen charging from the corrosion reactions.

Highlights

Titanium and its alloys play a predominant among the structural materials used for aerospace applications, owing to the benefits of weight saving, excellent corrosion resistance and good mechanical properties at moderate temperature (300-600°C)
Ti-6246 is an α+β alloy with high tensile strength at intermediate temperatures used in rotating components in the high pressure compressor stages of aero gas turbines
It was believed that AgCl can be generated by Ag lubricant reacting with a small amount of chlorine gas (< 1ppm) in the test environment, triggering Hot salt stress-corrosion cracking (HSSCC) above 380 °C [2]

Summary

Introduction

Titanium and its alloys play a predominant among the structural materials used for aerospace applications, owing to the benefits of weight saving, excellent corrosion resistance and good mechanical properties at moderate temperature (300-600°C). Ti-6246 is an α+β alloy with high tensile strength at intermediate temperatures used in rotating components in the high pressure compressor stages of aero gas turbines. Titanium can readily form a coherent and self-healing oxide film (mainly TiO2) on its surface, which results in the superior corrosion resistance in most circumstances. X-ray diffraction identified the presence of AgCl at the crack origin. It continues to be crucial to understand these cracking mechanisms to allow the safe design and operation of gas turbine Ti components

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