Reactive Forging − Pressure Assisted Thermal Explosion Mode of SHS for Processing Dense In Situ Composites and Structural Parts: A Review

Abstract

Over the last decades, there has been a decisive shift from basic science to applied research that brought about the development of a number of unconventional combustion processes that allow for simultaneous synthesis and consolidation of otherwise difficult‐to‐process high temperature materials. External pressure application during thermal explosion (TE) mode of self‐propagating high‐temperature synthesis (SHS) can produce dense products provided the combination temperature and pressure are sufficient for consolidation. In the developed TE‐based reactive forging (RF) method, a self‐sustained reaction is ignited by rapid heat transfer from press die and rams, and a moderate consolidation pressure is applied when the combustion product still contains a sufficient amount of liquid or very soft phase. Plastic flow of the product results in filling the shape of the die thus producing a near‐net‐shape part. Reactive forging (RF) is especially efficient in combination with the developed short distance infiltration (SDI) approach based on the presence of a low melting phase component (e.g., Al, Mg, Ti–Ni eutectics) in the non‐dense reactant blend that is squeezed into the pores under the applied pressure thereby increasing the interparticle contact area and enhancing exothermic heat release rate. Compared to traditional reactive melt infiltration, SDI has the advantage of the considerably shorter infiltration distances (μm vs. mm–cm). Close temperature monitoring during RF and RF/SDI processing provides a deeper insight into the SHS reaction mechanisms. The “heat sink” action of the pressure die after TE results in rapid cooling of the consolidated products and correspondingly fine microstructures and high mechanical properties. Examples of successful application of the RF/SDI processing of homogeneous and functionally graded in situ composites based on binary (Al2O3, TiB2, TiC, TiN) and ternary (MgAl2O4, Ti3SiC2, Ti3AlC2) ceramics, as well as intermetallic–ceramic and metal–ceramic interpenetrating phase composites are described. Nanostructuring of reactant blends results in lower SHS ignition temperatures, and thus can be utilized for two‐stage ignition of multi‐component composite materials and structures with tunable ignition delay. Pressure assisted SHS is a “green,” cost‐effective, and thus perspective manufacturing route of near‐net‐shape structural parts. Examples of successful application of RF and RF‐SDI approach to fabrication of ceramic matrix–diamond grinding wheels, light armor tiles and high melting temperature nozzles are presented.