Volume 109, Issue 4

The chemical vapor deposition (CVD) of TiCN and TiAlN coatings was investigated through thermodynamics calculations and key experiments. Based on the established CVD phase diagrams, TiCN coating was prepared by the low-pressure CVD method. It was found that the measured atomic fractions of C, N and Ti in the TiCN coating agree reasonably with the calculation results. For the TiAlN coating, CVD phase diagrams suggest that the deposition temperature and the ratio of AlCl 3 to NH 3 could remarkably affect the Al content in the coating. The present work leads to a better agreement with the experimental data than the previous calculations for Al content in the TiAlN coating. It is expected that the current work is of interest for further experimental investigations on CVD hard coatings.

In this work, Cr 3 C 2 and NbC grain-growth inhibitors are added simultaneously to control the grain growth of ultra-fine WC-10 wt.% Co cemented carbides. Several ultra-fine WC-10 wt.% Co cemented carbides with various contents of Cr and Nb are designed and fabricated by a hybrid approach of thermodynamic calculations and key experiments. According to thermodynamic calculation, the maximum additions of Cr and Nb are 0.65 and 0.4 wt.%, respectively, in order to avoid the appearance of detrimental phases M 7 C 3 and (Nb,W)C. The present experiments reveal that the density, transverse rupture strength, hardness and fracture toughness of WC-10 wt.% Co cemented carbides are improved significantly with the addition of Cr 3 C 2 and NbC below the maximum solubility in the binder phase. However, excessive Cr 3 C 2 and NbC lead to the formation of M 7 C 3 as well as coarse (Nb,W)C grains, which deteriorates the mechanical properties. The correlation between composition, microstructure, and mechanical properties is discussed from experimental and phase assemblage points of view.

The enthalpies of mixing in liquid alloys of the binary Mn–In and ternary Mn–In–Gd systems were determined over a wide range of compositions by means of isoperibolic calorimetry in the temperature range 1 500 – 1 650 K. The enthalpies of mixing in the Mn–In system demonstrate endothermic effects (Δ H max = 4.66 ± 0.38 kJ · mol −1 at x In = 0.40). The enthalpies of mixing in the liquid ternary Mn–In–Gd alloys were determined along six sections ( x Mn / x In = 0.22/0.78; 0.44/0.56; 0.65/0.35 and 0.83/0.17 for x Gd changed from 0 up to 0.5 and x Mn / x Gd = 0.30/0.70; 0.60/0.40 for x In changed from 0 up to 0.3). Enthalpies of mixing in the ternary system were found to be predominantly exothermic and steadily increasing in absolute values towards the Gd–In boundary binary system, reaching the maximum value in the vicinity of the phase GdIn.

The thermal stability of Nb–Cr–Mo alloy with the composition Nb-22.5Cr-2.5Mo (at.%), was studied by thermal exposure experiments in vacuum conditions at 1200 °C for 30 h, 50 h, and 100 h. The phase composition consists of Nb and C15 NbCr 2 , and the vast majority of alloying element Mo is found in the Nb matrix not in NbCr 2 particles. The grain size of Nb matrix exhibits a certain degree of growth during the thermal exposure process, while the grain size of NbCr 2 has no obvious change due to its high thermal stability. After thermal exposure at 1200 °C for 100 h, the alloy keeps its higher strength by the solid solution strengthening effect of Mo and the dispersion strengthening of NbCr 2 particles. At the same time, it has good plasticity due to dislocation slip in the Nb matrix and the emergence of stacking faults, twins and partial dislocations in NbCr 2 particles.

The effect of processing parameters on the grain refinement of vanadium nitrogen microalloyed steel was investigated by performing hot deformation tests. The interaction between static recrystallization and precipitation was analyzed and the effect of final temperature, cooling rate and holding time on the microstructure of the tested steel is discussed. The results showed that smaller ferrite grains could be obtained with lower temperature or higher cooling rate. It was found that carbonitrides could precipitate at temperatures around 850 °C, which could retard recrystallization. The precipitated particles could inhibit grain growth and promote ferrite nucleation, which leads to ferrite grain refinement. Therefore, fine ferrite grains could be obtained by performing multi-pass compression testing at this specific finishing temperature followed by appropriate holding.

The present study aimed at investigating the effects of different additives and heat treatments on the mechanical properties of Al-2.4 %Cu-1.2 %Si-0.4 %Mg-0.4 %Fe-0.6 %Mn alloy, a casting alloy intended for automotive applications. The research was accomplished through a study of the tensile properties in both as-cast and heat-treated conditions, where the effects of different heat treatments, i. e., T5, T6, T62 and T7, commonly applied to aluminum casting alloys were evaluated at ambient and at high temperature (250 °C), using different holding (stabilization) times at testing temperature. Six alloys were prepared using 0.15 wt.% Ti grain-refined alloy – considered as the base alloy B0, and alloys B1 and B2, and D0, D1, and D2 containing various amounts of Ni, Cr, V, Zr and La, added individually or in combination. The D-series alloys had a higher Si content of 8 wt.%. The results showed that T6 and T62 treatments provide the best improvements in strength at room temperature. At high temperature, the tensile properties vary depending on the stabilization time and heat treatment. The best alloy quality is provided by B1 and D1 alloys in T62 (444/368 MPa) and T7 (430/360 MPa) conditions, respectively.

Al–Si Gasar were produced using the metal–gas eutectic process. Directionally solidified porous Al–Si alloys with varying Si content were prepared by using a mold casting technique under different values of hydrogen saturation pressure. The influence of Si content on pore formation was studied; specifically, shape, size, porosity, circularity, and distribution along the height of the specimen were investigated. We observed that at increased levels of Si content, pores become more spherical and larger in diameter, while porosity decreases. Specimens produced by using different casting techniques exhibit differences in porosity, pore shape, and the relationship between porosity and the alloys’ Si content. Compression tests were performed to compare the mechanical properties of bulk alloys with porous, Gasar alloys.

The effect of addition of multi-walled carbon nanotubes (MWCNTs) on the wear behaviour of glass/epoxy composites manufactured using the pre-preg method was investigated. The MWCNT filling rates were 0.5, 1, and 2 wt.%, and unfilled composite samples were used for comparison. The worn surfaces were characterised by means of scanning electron microscopy for evaluating the wear mechanisms. The experimental results showed that all the composites filled with MWCNTs have a lower wear loss than the unfilled composite sample, and the wear resistance increased with increase in the amount of MWCNTs. It is revealed that the abrasive wear resistance of the glass/epoxy composites is mainly related to the adhesion at the matrix and fibre interface.

Cu–TiC x -bonded diamond composites were prepared by in-situ reaction sintering of Cu, Ti 3 AlC 2 , and diamond powders. The effect of Ti 3 AlC 2 content on the phase composition, microstructure, and grinding properties was investigated. Ti 3 AlC 2 was decomposed to TiC x and Al. Then, Al was dissolved into the crystal lattice of Cu to form a Cu(Al) solution. A carbon-rich transition layer was formed at the interface between the diamond and the matrix. Excess Al inhibited the formation of Cu solid solution and reacted with Cu to form Cu 3 Al 2 . Diamond may be damaged to some extent by adding excess Ti 3 AlC 2 in the raw materials, which may deteriorate the grinding performance of the composites. The grinding ratio value of copper–diamond composite was only 132, whereas that of the composites containing higher Ti 3 AlC 2 content in the raw materials was approximately 350.

This paper presents the fabrication of nanoceramic layers by electrophoretic deposition. Suspensions containing TiO 2 nanoparticles were prepared in different organic solvents, such as ethanol, methanol, acetone, and acetylacetone. During electrophoretic deposition, the color of organic media at around 200 V cm −1 began to change. This phenomenon is related to the anodic dissolution, which may assist deposition processes in some cases. Deviation from Hamaker's equation was observed upon measuring the deposited mass using different anode electrodes. Atomic absorption spectroscopy was used to measure concentrations of chemical elements liberated in the suspension due to the dissolution of anodes. These results show that anodic dissolution directly affects deposition rate. We observed this event even in the absence of powder and additives. Therefore, this is advantageous if anodic contaminants are not effective or influential.

The [Zr(OH) 5 ] − imidazolium complex was used to synthesize a zirconia precursor with plate-like nanostructue hydrolyzed under strong acid conditions, which was characterized by means of powder X-ray diffraction, thermogravimetric-differential scanning calorimetry, Fourier transform infrared spectroscopy, Raman spectroscopy, elemental analysis, inductively coupled plasma and electronic differential system. The zirconia precursor can be transformed to monoclinic ZrO 2 by annealing at a temperature above 400 °C. With the increasing of the curing temperature, it tended to give rise to porous ZrO 2 nanostructures.

Tri-layered brass steel/brass laminated composites were fabricated through hot dipping as well as casting. The chosen temperatures for hot dipping were 1 150 °C and 1 350 °C and for casting was 1 150 °C in addition to performing a heat treatment cycle at 900 °C for 90 min. The characterization results revealed that in the as-cast and the heat-treated samples, the formation of Fe-Zn intermetallic compounds occurred. In addition, with increasing the hot dipping temperature, stronger interfaces were achieved due to easier diffusion at higher temperatures. Moreover, casting without heat treatment was enough to obtain good bonding since the amount of Fe 3 Zn 10 intermetallic compound increased and grain growth occurred.