O. Jiménez

Effect of laser shock processing on erosive resistance of 6061-T6 aluminum

Abstract Application of laser shock processing (LSP) on 6061-T6 aluminum was made in order to evaluate its response to the erosive wear by silica sand. Impact angles of 15°, 30°, 60° and 90° were tested, two particle speeds (37 and 58 m/s) and two LSP irradiation conditions were used. Erosion marks were characterized by 3D profilometry and SEM analysis was conducted to identify the erosion mechanisms for each tested angle. The results showed a maximum erosive wear at low impact angles (ductile type behavior). Erosion strength and the erosion mechanisms were not affected by the application of LSP and they were attributed to the high strain rate of the erosion phenomena. A few differences encountered on the erosion plots were explained on the basis of the surface roughness left by the LSP process. The maximum mass loss and the maximum erosion penetration happened in different impact angles (15° and 30°, respectively). Finally, a well-defined erosion mechanism transition was observed, from cutting action at low impact angle, to crater formation at 90° of incidence.

Investigation of the effect of inert inclusions on densification during solid-state sintering of metal matrix composites

Abstract Solid-state sintering is the most used process to produce composites. In this paper, the effect of inert inclusions on densification during sintering was evaluated for Cu-WC and Cu-W composites, which have several industrial applications. Dilatometry tests were performed to follow the densification of composites. The effects of the quantity, size, and interphase bonding on densification of the matrix were studied. Distribution of the inert particles inside of the matrix was observed by scanning electronic microscopy. The results show that densification is decreased as the volume fraction of inclusions increases. Two different behaviors are detected when two different sizes of inclusions are used. For <20% vol. of inclusions, smaller tungsten particles have a minor effect on the densification than those of tungsten carbide. On the contrary, higher volume fractions of smaller tungsten particles drastically decrease the densification. The microhardness of the copper matrix is improved up to 15% vol. of inclusions, being higher for tungsten carbide particles. It was found that 15% vol. of inclusions is the maximal quantity of inclusions that can be used, as higher quantities inhibit densification and reduce the mechanical properties of the composite.

Sintering behaviour and mechanical characterisation of Ti64/xTiN composites and bilayer components

ABSTRACT Ceramic particle reinforcement can be used to improve the surface properties of Ti6Al4V (Ti64) alloy. Powder metallurgy route is a promising method to fabricate such reinforced Ti64 components. To assess the relevance of this technique, this work investigates the effect generated by the addition of TiN particles in Ti64 powder during free sintering. TiN reinforcement particles were randomly distributed in the Ti64 matrix with three different concentrations in two configurations: completely reinforced and unreinforced–reinforced bilayer. Dilatometry was used to obtain the shrinkage kinetics of samples at 1200, 1300 and 1400°C under inert atmosphere and to investigate the impact of reinforced particles on the sintering behaviour. The microstructure of sintered materials was shown to be lamellar in the unreinforced material and equiaxed in reinforced materials. Finally, the Vickers microhardness measurement showed the huge benefit of adding TiN particles to increase the mechanical strength of the Ti64 alloy.

Characterization of Constrained Sintering of Powders on Solid Substrate

Nowadays, sintering is a very useful technique to fabricate metal, ceramic and composites parts for different applications. This phenomenon has been extensively studied over 50 years and, most of the research related to it used a model based on two contacting particles. However, just a few jobs were focused on the powder sintering on a solid substrate. This work investigates the effect of two parameters; substrate shape and inclusion of the reinforced particles on the evolving microstructure during sintering of particles on a rigid substrate. Powders and solid bars of copper are used as a model material and particles such as tungsten carbide (WC) as reinforcing particles. Sintering was performed in an electrical furnace at 1050 °C under reducing atmosphere. The progress on sintering was evaluated by measuring the relative density close and far from the solid substrate by means of the image analysis from pictures taken by scanning electronic microscope (SEM). The effects on the constraint sintering were also identified. Heterogeneous densification and delamination of the film from the substrate were observed as densification increased which by the way is reduced by the inclusion of the reinforced particles.

Constrained sintering and wear properties of Cu-WC composite coatings

Abstract Coatings of metal matrix composites (Cu-WC) were fabricated by solid-state sintering. WC reinforcing particles in different quantities from 5% up to 30% (volume fraction) were mixed with Cu particles. After mixing, the powders were poured onto the surface of copper substrates. Sintering was carried out at 1000 °C under a reducing atmosphere in a vertical dilatometer. Sintering kinetics was affected by both rigid substrates and WC particles which retarded the radial and axial densification of powders. However, the coatings were strongly attached to the substrate, and WC particles were randomly distributed within the matrix. The addition of the reinforcing particles enhanced the microhardness and reduced the volume loss in wear tests to 1/17 compared to the unreinforced sample. The predominant wear mechanism was identified as abrasion at a load of 5 N. 20% WC (volume fraction) reinforcing particles led to the maximum values of properties for the composite coating.

Heat treated twin wire arc spray AISI 420 coatings under dry and wet abrasive wear

The influence of applying two different heat treatments such as: deep cryogenic and tempering on dry/wet abrasive wear resistance of twin wire arc spray martensitic AISI 420 coatings was evaluated by using a modified rubber wheel type test apparatus. A load dependency was observed on the abrasive wear rate behavior of both; dry and wet tests. Three body (rolling) and two body (sliding) wear mechanisms were identified in dry conditions, prevailing rolling at lower and higher loads. However, at higher loads, more presence of grooving and pits formation was observed. Coatings tempered at 205 °C/1 h displayed better wear resistance than cryogenic treated ones. A change in wear mechanism between dry and wet conditions was observed; two body wear mechanism predominated respect to three body. In both; dry and wet conditions the microstructure (several inter-splat oxides) as well as strain and residual stress promotes brittle material removal which was more evident in cryogenic and as-sprayed samples during dry test and at higher loads in wet conditions.

Sintering kinetics of Ni2FeSb powder alloys produced by mechanical milling

Abstract A ternary Ni 2 FeSb shape memory alloy was fabricated by powder metallurgy route. Sintering kinetics was estimated from dilatometry tests; whereas the microstructure and morphology of the powder and consolidated bulk samples were evaluated by XRD and SEM, respectively. Microhardness tests were performed on the surface of sintered samples. The results indicated that milling time has an effect on the shape and particle size as well as the homogeneity of the crystalline structures of the powders. Samples with longer milling time presented higher relative densities, better distribution of the elements on the alloy as well as the L2 1 and martensite phases, which will give the shape memory effect. The estimated activation energy values ranged from 109 to 282 kJ/mol at temperatures between 750 and 1273 K, indicating that sintering is controlled mainly by volume diffusion. Microhardness was improved by increasing the milling time and the heating rate.