This article presents a review of the current research into the diamond retention capacity of metal matrices, which largely determines the service life and working performance of diamond tools. The constitution of diamond retention capacity, including physical adsorption force, mechanical inlaying force, and chemical bonding force, are described. Improved techniques are summarized as three major types: (1) surface treatment of the diamond: metallization and roughening of the diamond surface; (2) modification of metal matrix: the addition of strong carbide forming elements, rare earth elements and some non-metallic elements, and pre-alloying or refining of matrix powders; (3) change in preparation technology: the adjustment of the sintering process and the application of new technologies. Additionally, the methods used in the evaluation of diamond retention strength are introduced, including three categories: (1) instrument detection methods: scanning electron microscopy, X-ray diffractometry, energy dispersive spectrometry and Raman spectroscopy; (2) mechanical test methods: bending strength analytical method, tension ring test method, and other test methods for chemical bonding strength; (3) mechanical calculation methods: theoretical calculation and numerical computation. Finally, future research directions are discussed.

https://www.mdpi.com/2075-4701/8/5/307/pdf

A Review of the Diamond Retention Capacity of Metal Bond Matrices

A series of silicon carbide-based ceramics with different sintering additives were liquid-phase sintered to high densities. Yb2O3 in combination with AlN was used as the additive, instead of the commonly used Y2O3–AlN, to improve the refractoriness of the secondary phase. Thermo-chemical decomposition of AlN was sufficiently suppressed with the use of nitrogen overpressure and reasonable weight loss was achieved in the different additive containing SiC ceramics without a reactive powder bed. Use of the heavier rare-earth element modified the liquid phase formed during sintering and reduced the phase transformation controlled grain growth rate, compared with Y2O3 doped materials. It also permitted microstructure tailoring through post-sintering heat treatments in nitrogen. Materials with self-reinforced microstructures, formed as a result of anisotropic grain growth, were obtained. Improved fracture toughness (4.5–5 MPa/m 1/2 ) and good flexural strength retention up to 14001C were also observed.

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Effect of Liquid Phase Sintering on Microstructure and Mechanical Properties of Yb2O3-AlN Containing SiC-Based Ceramics

https://apps.dtic.mil/sti/pdfs/ADA522083.pdf

Small Fatigue Crack Growth and Failure Mode Transitions in a Ni-Base Superalloy at Elevated Temperature (Preprint)

The synthesis and thermal expansion of metal coatings containing phase change material (PCM) prepared by electrolytic deposition were investigated. Such a composite combines the thermomechanical properties of the PCM with the high thermal conductivity of the metal, and can be used as a thermal actuator material. This study used paraffin as the PCM and copper as the metal matrix. The paraffin was first microencapsulated by emulsion polymerization to obtain microcapsules with a diameter of 1-5 μm containing 90 vol% paraffin to facilitate the incorporation of paraffin in copper by electrocodeposition. The microcapsules were added to a copper sulfate bath up to a concentration of 500 g/L. The electrocodeposition was performed at room temperature with a current density between 2 and 5 A dm -2 . These composites were examined by scanning electron microscopy, differential scanning calorimetry, and vertical dilatometry. Coatings with 40 vol % of microcapsules and a heat capacity of 12 kJ kg -1 during phase transformation were obtained. The thermal expansion of the composite showed a sharp increase in a small temperature range above the melting point. Although this behavior is ideal for thermal actuators, the effect decreased by thermal cycling. This remarkable thermomechanical behavior is explained by a thermoelastoplastic model for two-phase composites.

Synthesis and Characterization of Composite Coatings for Thermal Actuation

This paper discusses the influence of Particle Stimulated Nucleation (PSN) on the overall process of nucleation and subsequent grain growth in low carbon (LC) steels and proposes a global recrystallisation kinetics model based on fundamental physical metallurgy principles. The model takes into account the cementite content, which depends on the nominal carbon content, and the second phase particle size. The deformation field around cementite particles and its influence on processes is analysed. Finally, experimental evidence is given to show the accuracy of the theoretical predictions.

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Global recrystallisation model of low carbon sheet steels with different cementite contents

When the fabrication of a metal-matrix composite (MMC) involves its cooling from a high temperature stress-free state, plastic-elastic residual deformation fields can be generated within and around the particles due to the differential thermal expansion between the particle and matrix material. These residual fields are obtained for the situation where the particles are spherical, of equal radius and randomly distributed in the matrix. The solution is derived by embedding a composite sphere, consisting of an inclusion particle surrounded by a spherical shell of matrix material, within an effective medium. Specific results are presented for the Al/TiC MMC that illustrate the development during cooling of these residual fields and their dependence on the concentration of the TiC particles.

R. Bullough

Papers

The residual deformation fields in particle reinforced metal-matrix composites