Tape casting and reaction sintering of titanium-titanium oxide-nickel oxide mixtures

Suspensions of a powder mixture of titanium–titanium oxide–nickel oxide were tape cast. Analysis of the green tape showed an increase in Young's modulus and tensile strength with increasing powder volume content up to 28 vol%; at higher the properties decreased due to the formation of flaws in the green tape. The elongation of the green tape decreases continuously with increasing . Green tapes were laminated and were reactively sintered at 1350 °C to form a composite of TiO–NiTi2–Ni3Ti with a porosity of 5%. The wetting of TiO by NiTi2 prevented the TiO grains of forming a highly connected network, despite TiO making up 50% of the volume. The mixed intermetallic phases NiTi2 and Ni3Ti did form a continuous network. The three point bending strength of the composites was 121 MPa

Aqueous tape casting of reaction bonded aluminium oxide (RBAO)

Reaction bonding of alumina (RBAO) has been proved to be a successful route to make high-performance alumina. However, the aluminium metal in the starting mixtures prevents using aqueous processing techniques in the initial phase. Here a route is presented for aqueous tape casting of RBAO by hydrophobization of the starting powder and preparing a suitable tape cast suspension. Thermal analysis (TGA/DSC) showed that it is possible to combust the organic phase prior to oxidation of the aluminium, opening routes to laminated ceramic-metallic composites. TGA/DSC combined with imaging (SEM) and phase analysis (XRD) also showed that the oxidation of the aluminium in RBAO occurs in two steps. Sintering experiments showed anisotropic grain growth at 1550 °C, resulting in a lower density than sintering at 1500 °C or 1600 °C. The bending strength of the sintered tape increased with temperature, resulting in a bending strength of 290 MPa after sintering at 1600 °C

Aqueous tape casting of reaction bonded aluminium oxide (RBAO)

Reaction bonding of alumina (RBAO) has been proved to be a successful route to make high-performance alumina. However, the aluminium metal in the starting mixtures prevents using aqueous processing techniques in the initial phase. Here a route is presented for aqueous tape casting of RBAO by hydrophobization of the starting powder and preparing a suitable tape cast suspension. Thermal analysis (TGA/DSC) showed that it is possible to combust the organic phase prior to oxidation of the aluminium, opening routes to laminated ceramic-metallic composites. TGA/DSC combined with imaging (SEM) and phase analysis (XRD) also showed that the oxidation of the aluminium in RBAO occurs in two steps. Sintering experiments showed anisotropic grain growth at 1550 °C, resulting in a lower density than sintering at 1500 °C or 1600 °C. The bending strength of the sintered tape increased with temperature, resulting in a bending strength of 290 MPa after sintering at 1600 °C

Near-Net-Shape Ceramics by Reactive Processing

Since conventional production of high-temperature materials involves high investments and costly consumption of both energy and time, reaction engineering methodology combined with near-net shaping is often the answer to problems associated with the fabrication of advanced materials. Over the last decades, the number of different reaction-based processing methods for near-net-shaped ceramics has gradually increased. In this review, different reactive processing techniques and their potential for near-net-shaping are treated, e.g. SHTS (self-supporting high temperature synthesis), the Lanxide method DIMEX, reaction bonding (RB), reactive processing of Alumina-Aluminide Alloys (3A) and Al2O3-Al alloyed metal composites (3AMC).In addition to their potential for near-net shaping, other advantages to reactive processing routes are recognized to be reduced processing temperatures, reduced glassy phase formation at the grain boundaries, fine grained microsturctures and improved mechanical strength. Since the exothermic reactions constitute the base for reactive processing of high quality materials in an economic way, control of these reactions is essential. The process flows are described together with characteristic features of process and materials. In addtion, specific aspects of reaction-based synthesis will be illustrated with examples from own work in the area of reaction bonding of silicon nitride and alumina