In this study, Fe-Cr-C and Fe-Cr-W-C alloys are characterized using atom probe tomography. The alloys have been heat treated at 1070 degrees C for 30 min and subsequently at 780 degrees C for various time periods. Carbide formation is observed at each state. Cr-C precipitates smaller than 5 nm in radius for short heat treatment times and larger than 50 nm for heat-treatment times greater than 1000 s are observed. It is found that the phase interface moves during the first time period at an almost constant speed. Later on the velocity of the phase interface decreases. Furthermore, kinetic assumptions for carbide growth from a previous theoretical study have been verified. As expected, a decrease of the microhardness with increasing aging time is detected which is caused by martensite tempering. The aim of this study is to measure the change in chemical compositions across phase interfaces between matrix and precipitates to obtain a better understanding of the precipitation process.

Highlights • Effect of W fraction on pressureless densification of W–Si–C composites. • Full densification of high-W composite in a single PIP cycle. • High-W composite exhibits increase in thermal conductivity with temperature. • Low-W composites densified with six PIP cycles. • Low-W composites exhibit high mechanical and thermal properties. Abstract W–Si–C composites were fabricated by active filler controlled pyrolysis of W powder (high tungsten content) and W–SiC powder mixtures (low tungsten content), infiltrated by a preceramic polymer and heat treated at temperatures from 1600 to 2000 °C. Material with high volume fraction of W in initial powder–polymer mixture, formed a composite material composed of W, W2C and W5Si3 with closed porosity in a single polymer infiltration and pyrolysis (PIP) cycle. After heat treatment at 1700 °C the material exhibited flexural strength above 350 MPa, hardness of 7.8 GPa and indentation modulus of 250 GPa. Room temperature thermal conductivity of the composite was rather low, 23 W m−1 K−1, however, thermal conductivity increased with increasing temperature achieving 35 W m−1 K−1 at 1000 °C. The effect of W as active filler in W–SiC powder mixtures with low volume fraction of tungsten was negligible. Therefore, six polymer infiltration and pyrolysis cycles were used to achieve significant densification with 15% porosity. The material fabricated at 1800 °C was composed of SiC, WC and WSi2 and exhibited flexural strength of ∼400 MPa and room temperature thermal conductivity of 100 W m−1 K−1, which decreased to 32 W m−1 K−1 at 1000 °C. Graphical abstract

Highlights • For the first time, the C–W–Zr ternary system is described using the CALPHAD approach. • Experimental phase diagram data over the whole temperature and composition range are well reproduced by this modeling. • The complete liquidus projection, three-dimensional isometric view, and reaction scheme of the C–W–Zr system are presented. Abstract On the basis of critical evaluation of the literature data, the ternary C–W–Zr phase diagram has been assessed by means of the CALPHAD technique. The individual solution phases, i.e., liquid, fcc, hcp, bcc, and W2Zr have been modeled. The modeling covers the whole composition and temperature ranges. A self-consistent thermodynamic description for the C–W–Zr system has been developed. Comprehensive comparisons between the present calculations and measured phase diagrams show that the reliable experimental information is satisfactorily accounted for by the present thermodynamic description. The liquidus projection, three-dimensional isometric view, and reaction scheme of the C–W–Zr system have been presented.

The parameters for the electroplating process of Ni-Fe(Ti,W)C nanocomposite on the steel substrate were developed and optimised. for this purpose, the coating process was performed under a direct current using a nickel bath. The coating was fully characterised employing the X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy and microhardness tester. The results indicated that the Ni-Fe(Ti,W)C nanocomposite can be coated on the steel with an appropriate structure using the current density and the concentration of 40 mA cm−2 and 6 g L−1, respectively.

Abstract A kind of W/DLC/W–S–C composite film was fabricated by magnetron sputtering method. Effects of WSx content on the structure and the adhesion of the composite films were investigated. In addition, tribological behavior of the composite films was studied in the conditions of the ambient air and N2 gas atmosphere by ball-on-disk tester. The results indicate that the composite films show dense and amorphous microstructure. The WCx and WSx compounds are found in amorphous diamond like carbon matrix in the top layers of W–S–C. A proper WSx content is beneficial for improving the adhesion of the composite films. In air atmosphere, the composite films with high C content have better wear resistance and the friction coefficients range from 0.15 to 0.25. In N2 condition, high WSx content is benefit for the wear resistance and the friction coefficients of the composite films range from 0.03 to 0.1.

Abstract A kind of W/DLC/W–S–C composite film was fabricated by magnetron sputtering method. Effects of WS x content on the structure and the adhesion of the composite films were investigated. In addition, tribological behavior of the composite films was studied in the conditions of the ambient air and N 2 gas atmosphere by ball-on-disk tester. The results indicate that the composite films show dense and amorphous microstructure. The WC x and WS x compounds are found in amorphous diamond like carbon matrix in the top layers of W–S–C. A proper WS x content is beneficial for improving the adhesion of the composite films. In air atmosphere, the composite films with high C content have better wear resistance and the friction coefficients range from 0.15 to 0.25. In N 2 condition, high WS x content is benefit for the wear resistance and the friction coefficients of the composite films range from 0.03 to 0.1.