High Temperature Metal Matrix Composites Research Articles

A review on the scope of using calcium fluoride as a multiphase coating and reinforcement material for wear resistant applications

Solid lubricants play a vital role in the smooth and safe operation of many tribological industrial applications like cutting and forming tools, rolling and sliding contact bearings, gears, cams and protective coating in gas turbine engines for aerospace applications. Generally liquid lubricants are widely used for reducing the friction between the contacting parts which reduce the wear rate and increase the life of the parts. However, these liquid lubricants become useless when they are exposed to high temperature, high pressure and vacuum environmental conditions. Solid lubricants are those materials that can suitably reduce the friction and wear between the contacting or sliding surfaces that are in extreme environments like low and high temperature and pressure. Among the different types of solid lubricants, calcium fluoride is widely used owing to its excellent lubricity at elevated temperature. This paper initially describes the criteria for selecting solid lubricant and provides a comprehensive summary on calcium fluoride solid lubricant which can be used as a coating material in various high temperature metal and ceramic matrix composites for wear resistant applications. Further, investigations related to the selection of optimized coating parameters, synerging multiphase solid lubricants and soft metals with optimal percentage, selection of filler materials, mismatch in coefficient of thermal expansion and its impact on coating life are summarised and discussed. Finally, the scope of synthesizing calcium fluoride solid lubricant from discarded eggshell powders is explored.

Ytterbium Silicate Fibers: Fabrication, Microstructure and Strength

High temperature ceramic and metal matrix composites, which are to be used under complicated loading conditions in a severe atmosphere, have to satisfy a large number of the requirements. Hence, development of such composites calls for a large variety of fibers, matrices and interface materials to make an appropriate choice in designing a particular composite. The fiber is definitely the most important component of a composite. The family of oxide fibers is the most important among possible reinforcements for metal and oxide matrices. In this work, a family of potential oxide reinforcements containing ytterbium monosilicate Yb2SiO5 and disilicate Yb2Si2O7, and ytterbia-ytterbium monosilicate eutectic, was obtained and studied. The interest in those silicates was aroused because (i) they are highly resistant to hot corrosion in the presence of water vapor and (ii) their CTE varies from 8 × 10−6 K−1 for monosilicate to 4 × 10−6 K−1 for disilicate.

Computational simulation of microfracture in high temperature composites

This paper presents a summary and typical results of the research activities pertaining to composite microfracture in high temperature metal matrix composites carried out by the authors. The various failure modes and their effect on macro behavior as well as the hierarchy of their occurrences are examined by computationally simulating these events using three-dimensional finite element analyses. The procedure is based on the macro strain energy release rate which predicts the direction of crack growth and establishes the hierarchy and sequence of respective failure modes. Step-by-step procedures are outlined for evaluating composite microfracture. Microfracture results for various loading cases for a unidirectional metal matrix composite are presented and discussed. A key result is that interfacial debonding is a consequence of either fiber or matrix fracture.

Characteristics of a continuous Si-Ti-C-O fibre with low oxygen content using an organometallic polymer precursor

A continuous Si-Ti-C-O fibre with 12 wt% oxygen content, which is lower than the usual 18 wt% found in the normal fibres, was synthesized by using polytitanocarbosilane which has fewer Si-Si bonds than the usual precursor polymer. The density, tensile strength, tensile modulus and thermal conductivity were found to be 2.37 g cm−3, 3.4±0.3 GPa, 190±10 GPa and 1.40 W m−1 K−1, respectively. Amongst these properties, the tensile modulus was improved by 20 GPa and the thermal conductivity had a higher value in comparison with that of the ordinary Si-Ti-C-O fibre with 18 wt% oxygen content. The Si-Ti-C-O fibre with a 12 wt% oxygen content has a better heat resistance above 1400 °C in an argon atmosphere and 1300 °C in air, than the usual fibre. About 60 and 40% of its tensile strength at room temperature were retained in air at respectively, 1500 and 1600 °C. This improved ceramic fibre is considered to be useful as a reinforcing material for advanced composites such as high-temperature ceramic matrix composites and metal matrix composites.

Evolution of a metastable FCC solid solution during sputter deposition of TiAlB alloys

The microstructure evolution of a nominally αTi7Al7B alloy synthesized by sputter deposition has been examined. A highly supersaturated metastable single phase solid solution with a face centered cubic structure was identified as being the only phase present in the as-sputtered material. In contrast, Ti7Al and Ti7B alloys sputtered under the same conditions were also single phase but exhibited the expected hexagonal structure of α-Ti. The selection of the fee phase is based solely on kinetics, as the thermodynamically favored phase is always α (hcp). The reasons for the kinetic bias, however, are not clear. Annealing of the Ti7Al7B sputtered film at 900 °C for 1 h yielded precipitation of nano-scale TiB dispersoids in a single phase α-Ti matrix. Preliminary hardness and microstructural stability results of the dispersion unveiled promising potential for use of the physical vapor deposition technique to deposit TiB strengthened Ti-matrices on fibers in high-temperature metal matrix composites.

Probabilistic methods for the analysis of metal-matrix composites

A probabilistic micromechanics-based non-linear analysis procedure is developed to predict and quantify the variability in the properties of high-temperature metal-matrix composites. Monte Carlo methods and assumed probabilistic distributions of the constituent level properties including fiber, matrix, and interphase properties, volume and void ratios, strengths, fiber misalignment, and non-linear empirical parameters are used to predict the resultant ply properties and quantify their statistical scatter. Graphite/copper and silicon-carbon/titanium-aluminide (SCS-6 T115) unidirectional plies are considered to demonstrate the predictive capabilities. The non-linear material response of continuous-fiber-reinforced metal-matrix composite structures has also been studied by using the macroscopic elastoplasticity theory and a continuum shell element. The procedures discussed have a high potential for use in material characterization and selection (to precede and assist in experimental studies) and determination of the structural response of new high-temperature metal-matrix composites.

Micro-fracture in high-temperature metal-matrix laminates

Computational procedures are described to evaluate the behavior of high-temperature metal-matrix composites. Typical results are presented from studies done on compliant layers to reduce the residual thermal micro-stresses and the effect of partial bonding on composite properties. A three-dimensional finite element analysis in conjunction with strain energy release rates is also described to evaluate composite microfracture. Typical results for micro-fracture in composites subjected to thermo-mechanical cyclic loading are discussed and presented. The results show that interfacial debonding follows fiber or matrix micro-fracture.

The stability of interfaces in high-temperature metal-matrix composites

The interface between the matrix and the reinforcement is an area of great importance in the design of viable high-temperature metal-matrix composites (MMCs). Thorough understanding of the phenomena taking place at the interface is necessary to ensure reliable performance, but the thermodynamic data that would help to predict interfacial reactions are lacking for many systems. However, given certain knowledge, interfaces can be classified according to their stability, providing a tool for composites designers and an impetus for further fundamental work. This article describes the classification system and provides examples of interfacial behavior in a titanium-based material.

Reinforcement Considerations for High Temperature Metal Matrix Composites

Reinforcement Considerations for High Temperature Metal Matrix Composites

An apparatus for pressure casting of fibre-reinforced high-temperature metal-matrix composites

Liquid metal infiltration techniques for producing metal-matrix composites offer economic advantages. To date metal-matrix composites produced by casting have been limited to low-temperature metals such as Al, Mg and Pb because of the serious problems inherent in high-temperature casting. A technique and apparatus is described which has permitted the production of fibre-reinforced NiAl/Al2O3 and Ni3Al/Al2O3 composites. The technique involves liquid metal infiltration of Al2O3 fibres under gas pressure.

Materials Research and Applications at NASA Lewis Research Center

The facilities and instruments of the Lewis Research Center specialized for materials research are discussed. The main objectives of the Center are to provide R & D relevant to main propulsion plants and auxiliary power systems for aeronautics, space, and energy conversion applications. The Center is concerned with microstructure-property relations and their effect on processing; intermetallic compounds and high temperature metal matrix composites; ceramics with improved reliability for use in heat engines; polymer matrix composites for aerospace applcations; understanding the high temperature corrosive attack in the hostile environments of aircraft, rockets, and other heat engines; high temperature lubrication and wear; and microgravity materials research. The various types of schemes and techniques, provided by the Center, for analyzing data are described.