# Atomic faulting drives exceptional toughness in low thermal expansion chromium alloys

## TL;DR

A new chromium alloy combines low thermal expansion with high toughness by using atomic faulting in layered structures, making it suitable for extreme environments.

## Contribution

The alloy's exceptional toughness and low thermal expansion are achieved through atomic faulting in layered Cr2B precipitates.

## Key findings

- The Cr96Fe4Ge1.3B1 alloy exhibits low thermal expansion (αl = 1.79 × 10-6 K-1) and high toughness (240.2 J·cm-3).
- Layered Cr2B precipitates enhance mechanical properties by promoting atomic faulting and work-hardening.
- Antiferromagnetic fluctuations in the BCC matrix contribute to the alloy's low thermal expansion behavior.

## Abstract

Endowing functional properties with mechanical responses in traditional metals has been a frontier topic, akin to transforming base metal into gold. Chromium and its alloys, with their functional deficiencies and limited ductility, serve as typical examples. Herein, we report a Cr96Fe4Ge1.3B1 alloy that unifies low thermal expansion (LTE, αl = 1.79 × 10-6 K-1, 200 − 315 K) with exceptional toughness (240.2 J·cm-3). The enhancement in mechanical responses is primarily attributed to layered Cr2B intermetallic precipitates, which ameliorate interfacial cohesion and simultaneously refine the grain structure. The weakened interlayer interactions within the Cr-B layers facilitate the nucleation and movement of numerous tiny stacking faults in precipitates, efficiently alleviating strain energy and resulting in marked work-hardening ability. Additionally, antiferromagnetic fluctuations in the BCC matrix contribute to the unique LTE behavior. This paves the way for the design of high-performance alloys featuring layered-symmetry precipitates.

A low thermal expansion chromium alloy overcomes inherent brittleness via atomic faulting in layered precipitates. This tough, corrosion-resistant material enables stable components for extreme environments.