Research status of thermal damage inhibition technology for diamond

Significance: As the hardest material, diamond is widely used in various cutting and grinding tools. During the preparation process of diamond tools, thermal damage to diamonds is almost inevitable. The thermal damage to diamonds primarily includes graphitization, breakage, cracking, and chemical erosion. Graphitization of diamonds is a lattice transformation process of C atoms essentially, which requires sufficient energy to overcome the energy barrier. Consequently, during the preparation process of diamond tools, diamonds undergo varying degrees of graphitization due to high temperatures and catalyst elements. Breakage and cracking of diamonds primarily orginate from thermal mismatch between the diamond and the matrix metal, including its carbides, where carbides act as inducers of local residual stress, facilitating crack propagation. Chemical erosion of diamonds mainly refers to the process in which C atoms on the surface of diamonds react with active elements through diffusion during the sintering process, therefore deteriorating the diamonds. However, due to the poor wettability of diamonds, it often necessitates the addition of active elements such as Ti, Cr, V, etc., to react with diamonds and improve the holding force. Current suppression technologies for diamond thermal damage can be roughly divided into surface coating of diamonds, adjustment of matrix material properties, and optimization of forming technology. Progress: Diamond surface coating utilizes the unbonded atoms present on the diamond surface, which can react with certain elements at sufficiently high temperatures to form carbides, thereby enhancing the wettability between the matrix metal and the diamonds. Depending on the type of coating, it can generally be classified into metal and non-metal coatings. Metal coatings not only fill and repair defects in diamonds but also improve the bonding strength between the metal and diamonds. Common coating metals include Ni, Ti, W, Cr, and alloys are also selected as coating materials. For non-metal coatings, elements such as B and Si are typically chosen, as they can form carbide layers on the diamond surface, protect the diamond structure, reduce diamond oxidation, and prevent diamonds from being eroded and damaged by strong carbon elements in the matrix material. The choice of matrix material plays a crucial role in mitigating thermal damage to diamonds. Low-melting-point matrix materials can effectively reduce sintering temperature and inhibit the graphitization of diamonds consequently. Furthermore, incorporating appropriate active elements into the matrix material can enhance the interfacial strength between diamond and the matrix, thereby improving the performance of diamond tools. Currently, the modulation of matrix material properties is primarily focused on alloy optimization and composite material development. Alloy optimization aims to reduce diamond thermal damage by refining the alloy composition of the matrix material. Researchers have experimented with elements such as Si, Hf, and Zr, discovering that these elements can mitigate the erosion of diamonds by active elements and reduce diamond thermal damage. Additionally, amorphous Ni-based alloys, due to their low melting point and narrow melting range, have been used as brazing materials to enhance the performance of diamond tools. Composite material development seeks to improve mechanical properties while utilizing suitable reinforcing phases to absorb catalytic elements within the matrix, thereby reducing diamond graphitization. Additionally, reinforcing phases could optimize the diamond interface condition, leading to both increased interfacial strength and reduced diamond thermal damage. Molding technology significantly impacts the lifespan and performance of diamond tools, particularly through parameters such as molding temperature, soaking time, molding pressure, and atmosphere. Molding temperature and soaking time determine grain growth in the matrix, diamond thermal damage, and the interfacial growth between diamond and the matrix. Molding pressure affects the density of the matrix material, which in turn influences its mechanical properties. The atmosphere, typically vacuum or protective, must be carefully controlled, as even trace amounts of moisture or oxygen could lead to diamond oxidation, degrading tool performance and lifespan. Diamond tools are typically manufactured through methods such as hot-press sintering and brazing, while additive manufacturing is emerging as a promising direction in tool fabrication. Conclusions and Prospects: Future research to mitigate diamond thermal damage could focus on three main areas: theoretical analysis of diamond interfaces at the microscale, the establishment of a guidance system matching diamond tool matrix materials with service environments, and investigation of the mechanical behavior of diamonds interfaced during the molding process.