On the thermal shock resistance and mechanical properties of novel unidirectional UHTCMCs for extreme environments

Luca Zoli,Diletta Sciti,Cesare Melandri,Pietro Galizia,Antonio Vinci

doi:10.1038/s41598-018-27328-x

Abstract

Aerospace provides a strong driving force for technological development. Recently a novel class of composites for harsh environments, based on ultra-high temperature ceramic composites reinforced with continuous fibers (UHTCMC), is being developed. The goal of this work is to overcome the current data patchwork about their microstructural optimization and structural behavior, by showing a consistent mechanical characterization of well-defined and developed UHTCMCs based on ZrB2-matrix. The obtained composites have a density of 3.7 g/cm3 and porosity of less than 10%. The flexural strength increased from 360 to 550 MPa from room temperature to 1500 °C, showing a non-brittle behaviour. The composites were able to sustain a thermal shock severity as high as 1500 °C. The maximum decrease of strength at 1400 °C was 16% of the initial value, indicating that the samples could be shocked at even higher temperature. Flexural strength, Young’s modulus and coefficient of thermal expansions (CTE) of the composites were measured both along transverse and longitudinal direction and correlated to the microstructural features. The presented microstructural and mechanical characterization well defines the potentiality of the UHTCMCs and can be used as reference for the design and development of novel thermal protection systems and other structural components for harsh environments.

Highlights

The pursuit of new ultra-high temperature structural materials is driven by the ever present need to improve the efficiency of aerospace or power-generation gas-turbine engines by operating at higher temperatures
An alternative class of materials is represented by ultra-high temperature ceramics (UHTCs), such as the borides and carbides of early transition metals[2]
The most common approach adopted for the fabrication of Ultra-High Temperature Ceramic Matrix Composites (UHTCMCs) is the introduction of UHTC phase such as ZrC, ZrB2, TaC, HfC in C/C or C/SiC composites obtained by PIP or PIP/CVI method[3,4,5]

Summary

Introduction

The pursuit of new ultra-high temperature structural materials is driven by the ever present need to improve the efficiency of aerospace or power-generation gas-turbine engines by operating at higher temperatures. An alternative class of materials is represented by ultra-high temperature ceramics (UHTCs), such as the borides and carbides of early transition metals[2]. In this case the amount of UHTC phase is predominant in the matrix and SiC (if present) is a secondary phase[10]. Alternative approaches include the reactive metal infiltration process, where a Zr2Cu molten alloy reacts with Boron –impregnated Cf preform at temperatures of 1500 °C or higher The challenge of this process is the complete elimination of unwanted residual low melting phases[15,16] that even in very low amounts can compromise the high temperature stability. The process is remarkably fast and amounts to one working day for the production of the green composite and few hours for sintering

Objectives

Methods

Results

Conclusion