Key Takeaways & Executive Findings
- •• Deep cryogenic treatment (DCT) for 200 h increases residual stress in HIP beryllium by 59.9% due to non-uniform volumetric contraction and mismatch stress. • DCT induces grain refinement (12.3% decrease) and higher dislocation density (17.9% increase in GND), leading to improved yield and tensile strengths by 4.2% and 5.6%, respectively. • DCT significantly enhances dimensional stability: cumulative size changes during cold exposure and cold cycling are reduced by 86% and 50%, respectively, after 200 h treatment. • After room-temperature creep at 100 MPa for 1000 h, DCT-treated beryllium shows 12.5% higher residual tensile strength and 5.5% higher retention rate, indicating improved long-term reliability.
Abstract
This study investigated the effects of deep cryogenic treatment (DCT) on hot isostatic pressed (HIP) beryllium for inertial devices, focusing on residual stress, microstructure, tensile properties, and dimensional stability. The findings revealed that during DCT, residual stress in beryllium increased gradually due to non-uniform volumetric contraction and mismatch stress, reaching a 59.9% increase from initial levels after 200 h of DCT. DCT led to significant grain refinement and an increase in dislocation density. In 200 h DCT-treated beryllium, geometric necessary dislocation (GND) density increased 17.9%, grain size decreased 12.3%, and therefore yield strength and tensile strength improved by 4.2% and 5.6%, respectively. The dimensional stability of HIP beryllium was significantly enhanced by DCT, and the improvement tended to increase with the duration of DCT. The cumulative size changes of beryllium after 200 h of DCT during both cold exposure and cold cycling decreased significantly by 86% and 50%, respectively, compared to those of HIP beryllium. Furthermore, the residual tensile strength and retention rate increased by 12.5% and 5.5%, respectively, after undergoing room-temperature creep at 100 MPa for 1000 h.
1. Introduction
Due to its low density, excellent thermal conductivity, high specific stiffness, and good dimensional stability, beryllium is a key material for preparing gyroscopes and accelerometers for inertial navigation systems [1, 2]. In demanding scenarios such as aerospace [3, 4] and polar expeditions [5], beryllium components confront the challenges of extreme low-temperature environments. Thus, enhancing the dimensional stability under low-temperature conditions of beryllium has become imperative to ensure the stability and high accuracy of the overall instrument. Dimensional stability refers to a material's ability to maintain its original shape and size during long-term storage or service [6 −8], which is influenced primarily by residual stress relaxation and gradual microstructural changes [9, 10]. The existing methods, including annealing [11, 12] and thermal-cold cycling [13, 14], are primarily used to improve the dimensional stability under room temperature conditions. Therefore, it is necessary to explore a method to improve the dimensional stability of beryllium under low-temperature conditions.
Deep cryogenic treatment is the process of subjecting materials to extremely low temperatures (below −130 ℃) to modify their microstructure and properties [15, 16]. DCT enhances the mechanical properties and dimensional stability of steel through precipitation strengthening, dislocation strengthening, and grain refinement [17 −22]. Researchers such as LIU [17], VILLA [18] and GILL et al [19] have observed a substantial decrease in the conversion of austenite to martensite in steels, specifically AISI 52100 and AISI M2, after undergoing DCT. DAS et al [20] investigated the influence of DCT on carbides in AISI D2 and W6Mo5Cr4V2, observing an increase in carbide volume, smaller carbide size, and a more homogeneous dispersion. ZHANG et al [21] delved into the effects of DCT on M54 steel, noticing an augmentation in dislocation density along with corresponding hardening processes. CHENG et al [22] subjected S30408 stainless steel to DCT, discovering changes in grain size and an increase in low-angle grain boundaries. Similar results have also been reported in aluminum alloys [23, 24], and magnesium alloys [25, 26].
Although DCT has demonstrated notable advantages for different alloys, its potential effects on beryllium remain unexplored. Therefore, an investigation into the effects of DCT on beryllium's residual stress, microstructure, and mechanical properties is warranted. By elucidating the interplay among these alterations and assessing their potential to enhance beryllium's low-temperature dimensional stability, the study could contribute significantly to enhancing the reliable and steady performance of inertial devices.
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REN Peng-he, XIAO Lai-rong, ZHAO Xiao-jun, CAI Zhen-yang (2026). Effects of deep cryogenic treatment on microstructures, mechanical properties and dimensional stability of beryllium for inertial devices. Journal of Central South University. https://doi.org/10.1007/s11771-026-6204-7
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Frequently Asked Questions
What is deep cryogenic treatment (DCT) and how does it affect beryllium?
Deep cryogenic treatment (DCT) involves subjecting materials to extremely low temperatures (below -130°C) to modify their microstructure and properties. In beryllium, DCT increases residual stress due to non-uniform volumetric contraction, refines grains, and increases dislocation density, leading to improved mechanical properties and dimensional stability.
How does DCT improve the dimensional stability of beryllium?
DCT significantly enhances dimensional stability by reducing cumulative size changes during cold exposure and cold cycling. After 200 hours of DCT, the cumulative size changes decreased by 86% and 50% respectively, compared to untreated HIP beryllium.
What are the quantitative improvements in mechanical properties after DCT?
After 200 hours of DCT, yield strength and tensile strength improved by 4.2% and 5.6%, respectively. Additionally, residual tensile strength and retention rate increased by 12.5% and 5.5% after room-temperature creep at 100 MPa for 1000 hours.
Why is beryllium used in inertial devices and what challenges does it face?
Beryllium is used in inertial devices like gyroscopes and accelerometers due to its low density, high specific stiffness, and good dimensional stability. However, in extreme low-temperature environments, maintaining dimensional stability is challenging, which DCT helps address.
What is the significance of this study for aerospace and polar applications?
This study provides a method to enhance the dimensional stability of beryllium under low-temperature conditions, which is crucial for the reliable performance of inertial navigation systems in aerospace and polar expeditions, where extreme cold can affect material stability.
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