Titanium-based Composites Research Articles

Silicon carbide fibre-reinforced titanium base composites having improved interface properties

Silicon carbide fibre-reinforced titanium base composites having improved interface properties

Methodology for Prediction of Fiber Bridging Effects in Composites

A review of three different methods used at NASA Lewis to account for the effect of fiber bridging on fatigue crack growth (FCG) in metallic and intermetallic titanium-based composites is presented. Of the three methods, the fiber pressure model (FPM) was the only one able to accurately predict both crack opening displacements (CODs) and the FCG rates for both composites under the various applied loading conditions.

The tensioned push-out test for fibre-matrix interface characterisation under mixed mode loading

A novel test procedure is suggested for the exploration of interfacial mechanical properties in fibre-reinforced composites. This is based on the established single fibre push-out test, which has the advantage of being applicable to specimens which can be routinely produced from normal unidirectional long fibre composite materials. The suggested modification involves the application of equal biaxial in-plane tension while the push-out testing is carried out. This allows the interface to be subjected to various combinations of mode I and II loading, ranging from pure opening to pure shear. Hence it should be possible to obtain data characterising the resistance to interfacial debonding and disengagement over all of this range. Illustrative data are presented here for titanium-based composites, in the form of measured critical shear stresses for various applied normal stresses at the interface.

Cross-section TEM sample preparation of Ti-6Al-4V/SCS6 (SiC) fiber-reinforced composites

Titanium-based metal matrix composites (MMC) and titanium aluminide intermetallic matrix composites (IMC) have been selected for future aerospace structural applications. The mechanical integrity of these composites are dictated by the thermodynamic stability of the fiber / matrix interface and deformation that occurs at the interface. The thermal processing incurred during hot-isostatic-pressing (HIP) results in the formation of intermetallic phases, with detrimental mechanical properties, at the interface. In addition, the thermal processing results in residual stresses due to the mismatch in coefficient of thermal expansion (CTE) between the Ti-based matrix and the SiC fiber. In some cases the thermal stresses are sufficient to cause yielding in the matrix, and/or lead to fatigue from the thermal cycling that will be incurred during application.

Fiber-Matrix Interphase Effects upon Transverse Behavior in Metal-Matrix Composites

To develop reasonable analytical models and to understand better how the integrity of the fiber-matrix interface in high temperature titanium-based metal-matrix composites affects the overall transverse normal characteristics, a parametric study of various fiber-matrix interface conditions was performed. Analysis methods included both a simplified one-dimensional mathematical model and a finite element analysis using MSC/NASTRAN. First, both strong (perfectly bonded) and vanishingly weak (unbonded) interfaces were examined. Subsequently, to provide for partial bonding, a model that used an elastic-plastic interphase zone between the fiber and matrix was examined. It was found that the variation in the plastic properties (that is, yield stress and strain hardening) of this interphase zone provided the flexibility to model any level of interfacial bonding.

Investigation of diffusion barrier coatings on SiC monofilaments for use in titanium-based composites

The development of titanium-based composites has been hindered largely because of interfacial diffusion. When SiC is in contact with titanium at elevated temperatures, metal silicide (Ti 5Si 3) and carbide (TiC) are formed. The aim of our work is to reduce the fibre-matrix interaction at high temperatures by interposing compounds between the metal and SiC reinforcement. Procedures are described for the formation of thin layers on silicon carbide fibres (Sigma) by sputter deposition. Sputtering offers good control over density and stress state, thickness and composition. Past work has shown that sputtered Y 2O 3 deposited on SiC, SiCSi or metal can reduce the degree of ceramic-metal reaction. Use of the Gibbs free energy of formation of TiO 2 provides a simple basis for the assessment of this material for use in a titanium matrix. Since TiSi 2 and silicon are also present in the TiSi diagram, they could act as diffusion barriers. Coatings of TiSi 2, Y 2O 3 and ZrO 2 have been produced by sputter deposition. The stoichiometry of the coatings has been revealed by Rutherford backscattering spectrometry. Coated fibres have been used to prepare titanium-based composites by hot pressing. Annealing between 900 and 1100°C has been performed. Scanning microscopy, Auger electron spectroscopy and transmission electron microscopy have been used to investigate the interfacial products.

Method for continuous fabrication of fiber reinforced titanium-based composites: Siemers, P. A. (General Electric Company, Schenectady, NY, USA) US Pat 4 782 884 (2 November 1988)

Method for continuous fabrication of fiber reinforced titanium-based composites: Siemers, P. A. (General Electric Company, Schenectady, NY, USA) US Pat 4 782 884 (2 November 1988)

Thermal cycling of titanium-based composites reinforced by B(B4C) filaments

Experimentation d'un cyclage thermique qui combine les effets d'une exposition a la chaleur et d'un cycle thermique. Resultats obtenus sur des composites B(B 4 C)/Ti−6Al-4V

Electrical conductivity of aluminum and titanium base reinforced composites

1. For aluminum reinforced with steel fibers, increasing the fiber concentration to 50–60 vol. % produces only a small increase in the electrical resistivity of the composite. At higher fiber concentrations the rate of ascent of theϱ vs Vf curve sharply increases. 2. For titanium base composites reinforced with molybdenum fibers, at low reinforcing phase contents (of the order of 10–20 vol.%) the electrical resistivity of the composites decreases by a factor of more than 2 to 3 compared with the resistivity of the matrix. Subsequently, the rate of fall ofϱ slows down. 3. The experimental curves of resistivity vs composition and temperature for all the composites investigated are similar in character to the curves obtained analytically; however, the experimental values are slightly higher than the calculated results, by 3–4% for the aluminum base composites and by 10–12% for the titanium base composites.

Structure formation during the annealing of Ti-Cr3C2 composites

1. A study was made of structure formation during the annealing of titanium-base Ti-Cr3C2 composites. It is shown that during the annealing of extruded specimens at 950–1250°C the chromium carbide dissolves and a new phase, titanium carbide, is precipitated. An examination in a JSM-I3 scanning electron microscope established that the titanium carbide formed under these conditions is free from chromium, the reason for this being that the metallic matrix of the composite is in a state of disequilibrium. 2. Microhardness measurements were made on the structural phase constituents after annealing. The lowest value of titanium matrix microhardness was recorded for specimens annealed at 1150°C, a temperature at which titanium dissolves about 14% of chromium.