Chromium and chromium-based alloys: Problems and possibilities for high-temperature service

Abstract

Beyond Ni-Based Superalloys OverviewThis article presents an overview of publications on mechanical properties of chromium and chromium-based alloys, with particular emphasis on ductility at low temperature and strength at high temperature. Analysis of rather scattered data suggests that a chromium or chromium-based alloy can be ductilized at ambient temperature and is quite capable of being strengthened to high levels at high temperature. A new composition design and process would open new opportunities for chromiumbased alloys as structural materials used at temperatures up to 1,300°C.

Thermodynamic Assessment of Cr-Rare Earth Systems

“…Chromium is of particular interest due to ''good oxidation resistance, low density (20% less than most nickel-based superalloys) and high thermal conductivity (two to four times higher than most superalloys)''. [1] While efforts were made from the late 1940s to early 1970s to develop chromium-based alloys, two major mechanical disadvantages of chromium have hindered commercial exploitation of Cr alloys as major structural materials at high temperatures. These disadvantages are high ductile-tobrittle transition temperature (DBTT is about 150°C for unalloyed recrystallized chromium of commercial purity [1] ) and embrittlement in high-temperature environment due to oxidation and subscale nitridation.…”

“…[1] While efforts were made from the late 1940s to early 1970s to develop chromium-based alloys, two major mechanical disadvantages of chromium have hindered commercial exploitation of Cr alloys as major structural materials at high temperatures. These disadvantages are high ductile-tobrittle transition temperature (DBTT is about 150°C for unalloyed recrystallized chromium of commercial purity [1] ) and embrittlement in high-temperature environment due to oxidation and subscale nitridation. Creep strength is also of particular concern when chromium is intended for use as vanes or blades in gas-turbine engines especially due to the very low creep resistance of pure chromium.…”

Materials for Gas Turbines – An Overview

“…Since the late 1970s, chromium alloys received very little attention. In recent years there is a revival of interest in these alloys (Gu et al, 2004). Aims of the recent researches have been (i) improvement in high temperature strength (ii) protection from nitridation / oxidation embrittlement (iii) improvement in the impact ductility at ambient temperature.…”

“…Aims of the recent researches have been (i) improvement in high temperature strength (ii) protection from nitridation / oxidation embrittlement (iii) improvement in the impact ductility at ambient temperature. There have been some encouraging findings -(i) trace additions of silver can improve room temperature ductility significantly (ii) strengthening with intermetallics can improve high temperature strength (iii) substantial progress has been made in the area of high temperature coatings (Gu et al,2004). It is still a long way, however, before the engine manufacturers get interested in these alloys.…”

Chromium-Based Alloys Strengthened by Ordered Phase Precipitation for Gas Turbine Applications

“…High-temperature creep tests were carried out on compression specimens of as-cast RT4 and RT7 alloys. The dimensions of the specimens were 3x3x6 mm 3 . The creep tests were conducted at 1100°C by incremental step-loading under dynamic argon to prevent excessive environmental damage.…”