Volume 107, Issue 7

The interdiffusion behavior of bcc_B2 Ni–Al–Cu alloys at 1173 K was experimentally investigated on the basis of six groups of bulk diffusion couples. With the electron probe microanalysis technique and the Matano–Kirkaldy method, the composition-dependent mole-fraction interdiffusion coefficients and the interdiffusion fluxes in bcc_B2 Ni–Al–Cu alloys at 1173 K were determined. The reliability of the presently obtained interdiffusivities was verified by the thermodynamic stability constraints, comparison with the interdiffusion coefficients in boundary binary bcc_B2 Ni–Al alloys as well as numerical simulations based on Fick's second law.

Nanocrystalline and amorphous NdMg 11 Ni + x wt.% Ni ( x = 100, 200) composites were synthesized by mechanical milling, and their gaseous and electrochemical hydrogen storage kinetic performances were systematically investigated. Hydrogen absorption and desorption properties were investigated by means of a Sievert apparatus and a differential scanning calorimeter connected with an H 2 detector. Electrochemical hydrogen storage kinetics of the as-milled alloys were tested by an automatic galvanostatic system. Results show that increasing Ni content significantly improves gaseous and electrochemical hydrogen storage kinetics. The improved gaseous hydrogen storage kinetics of the alloys are ascribed to the decrease in hydrogen desorption activation energy caused by increasing Ni content and milling time.

Sn–Bi alloys form some of the common types of Pb-free solders. Au is used as one of the under bump metallization layers due to advantages such as corrosion resistance and anti-oxidation properties. Phase equilibria information plays a vital role in the development of materials technology and serves as an important tool to understand interfacial reactions at heterointerfaces. In this study, the phase equilibria in the Au–Bi–Sn ternary system were experimentally investigated at temperatures of 80, 125, and 150 °C. The results indicated that a ternary phase with a composition of Au 45 – 48 -Bi 36 – 38 -Sn 14–19 (at.%) was found in the Au–Bi–Sn ternary system at these three temperatures.

The aim of this work was to investigate the effects of current density, temperature, pH and concentration of ethylhexilsulfonate additive on the microhardness of electrochemically deposited gold decorative coatings obtained from a conventional cyanide electrolyte and gold complex based on mercaptotriazole. Mechanically and chemically prepared brass samples were first nickeled from acidic electrolyte. Nickel was a substrate deposit, and then decorative gold coatings were deposited from two types of electrolytes at different current densities and temperatures. Decorative gold coatings were deposited from auri-mercaptotrizole at different pH values and from electrolyte with and without the ethylhexilsulfonate additive. The microhardness of the gold coating was measured using the Knoop method. The highest values of microhardness were obtained at a current density of 1 A dm −2 at room temperature for both electrolytes. The microhardness of the gold coatings from cyanide electrolytes was HK = 740 MPa, and the coatings obtained from auri-mercaptotriazole HK = 660 MPa. This difference is not relevant for decorative purposes. The highest values of microhardness, HK = 660 MPa, were obtained at pH = 9 from the gold complex based on mercaptotriazole without the additive.

CoCrMo alloys are widely used as artificial joint implants due to their excellent mechanical properties, good wear resistance and outstanding corrosion resistance. However, the risks of release of cobalt and chromium ions urge researchers to improve the wear resistance of implants further by using surface modification technology. Diamond-like carbon film with 3.0 μm thickness was deposited on the surface of CoCrMo alloy using ion-source-assisted magnetron sputtering. The friction coefficients of the CoCrMo alloy decreased remarkably under different conditions after the formation of diamond-like carbon film. After the deposition of diamond-like carbon film the wear rates of the CoCrMo alloy decreased by 52.4 %, 47.1 % and 49.4 %, under dry friction, physiological saline, and bovine serum lubrication, respectively.

The article presents the influence of stationary plastic deformation, using the equal channel angular pressing (ECAP) method, on the structure and properties of an aluminium alloy with 3 % magnesium content. In order to investigate changes in the structure and substructure, light microscopy and transmission electron microscopy were used. The influence of plastic deformation was determined by hardness measurement using the Vickers method. The results of the investigation show that, even after one ECAP, it is possible to decrease grain size to a range of 30 – 70 nm, and increase the mechanical properties by nearly 90 %. It was also found that the additional twist angle of the die has a minor effect on the properties and structure of the investigated alloy.

Five ternary Zn-15Al-(1 – 5)Cu and six quaternary Zn-15Al-3Cu-(0.5 – 3)Si alloys were prepared by permanent mold casting for this work. Their unlubricated sliding friction and wear properties were investigated at a pressure of 3 MPa and a sliding speed of 1.5 m s −1 for a sliding distance of 2 500 m using a block-on-disc type tester. The friction coefficient and wear volume of the ternary alloys decreased with increasing copper content, but above 3 % Cu the trend reversed. As the hardness and both tensile and compressive strengths of the ternary alloys increased, their friction coefficient, working temperature and wear volume decreased. However, the trend reversed for the hardness and compressive strength of the quaternary alloys. The correlation between mechanical and tribological test results showed that the wear volume of Zn-15Al-based alloys can be determined in terms of their tensile strength.

Alumina foams with high mechanical strength were prepared by means of gel-casting. After preparation of gel-cast raw segments, they were dried in a controlled humidity chamber. Samples were sintered at a temperature of 1 350 °C held for 2 h. The effects of additives and alumina loading on the initial suspension behavior, ultimate porosity, relative density, and mechanical strength of sintered samples were investigated by means of different techniques including densitometry, scanning electron microscopy and compressive strength measurements. Results showed that the optimal conditions for the preparation of desired alumina foam are 0.03 wt.% of sodium dodecyl sulfate, 1 g L −1 of initiator and 8.3 mL L −1 of catalyst for suspensions with 0.8 – 1 wt.% of Tiron and 70 % of alumina loading. The value of compressive strength was measured as high as 25.62 MPa for alumina foam with very low relative density of 19.27 %.

Hybrid carbon nanotube–aluminum reinforced ZA27 composites under hot compressive forces were investigated in the temperature range of 473 – 523 K with strain rates of 0.01 – 10 s −1 . From the experimental data, the flow stress curves for increasing strain exhibit typical flow behavior associated with dynamic recrystallization softening. A comparison of predictions from an artificial neural network model and the constitutive equations to describe the hot compressive behavior was performed. Relative errors varied from −4.14 % to 6.75 % for the artificial neural network model and from −15.93 % to 17.29 % using the constitutive equations. The results indicate that the artificial neural network model was more accurate and efficient in predicting hot compressive behavior.

This work presents a computational method for the identification of the thermal conductivity of a powdered composite. The thermo-physical properties of powdered composites depend not only upon the intrinsic material properties of the filler and the matrix, but also upon several other parameters including the packing density, the particle shape factor and the particle size. In this paper, a genetic algorithm-based model is proposed for the identification of the effective thermal conductivity of a Bakelite–graphite powdered composite. A comparative analysis is also developed between the genetic algorithm and the experimental, theoretical and finite element results. In comparison with the experimental observations, the genetic algorithm model was found to have error values of approximately 5 %, whereas the errors resulting from the theoretical models were up to 12 %.

In this study, the structural properties and enhancement in the hardness of commercial WC–Co-based cemented carbide inserts are reported after the formation of a boronised layer on the surface. A boronising thermochemical treatment was given at 900 °C for 4 h. X-ray diffraction analysis verified the treatment in the presence of peaks associated with the Co 2 B and W 2 CoB 2 phases. The hardness of the samples used in the boronising process increased from 1492 HV up to 2000 HV. The typical values of the thickness of the boronised layer were measured to be around 28 μm. The results of a tool-life test suggest that boride coating effectively enhances the cutting performance of the samples.