Abstract: The wettability between liquid Ti-50Al (at.%) (TiAl) and calcia-stabilized zirconia (ZrO2 (CaO)) in the gravity field and/or electromagnetic fields was studied in argon atmosphere. The results show that the equilibrium contact angle between liquid TiAl and ZrO2 (CaO) decreased from 63° in the gravity field to 50° in the electromagnetic field. However, the time required for the system to achieve equilibrium in the electromagnetic field was 16s, which was longer than that in the gravity field. The effect of the electromagnetic field on the wettability between TiAl and ZrO2 (CaO) was explained by the total free energy at the liquid/solid interface and activity of Ti element.
Abstract: The study contains a complex method of forming the surface-modified layers using materials with shape memory effect by high-speed gas-flame spraying of mechanically activated powders based on TiNiHf, followed by thermal and thermomechanical treatment. This allowed us to form the nanoscale state in the surface layers, which have high levels of functional, mechanical and performance properties. We demonstrated that pre-mechanoactivation of TiNiHf powder has reduced the coatings' porosity (less than 1%) and provided adhesive strength of the coating with the substrate (110 to 120 MPa). We described the formation mechanism of nanostructured state in TiNiHf powders under severe plastic deformation during mechanical activation, comprising the steps of high-speed deformation, polygonization and recrystallization.
Abstract: The aim of this study is to evaluate the effect of phase formation to the mechanical strength of Ti-Nb alloy produced by powder metallurgy (PM) process. Niobium (Nb) powder was added to the elemental titanium (Ti) powder by wt%, cold-compacted and sintered at 1200°C. The samples were characterized in term of shape and sizes of the particle, phases present, microstructures and compressive strength. XRD pattern showed that increasing Nb content resulted in increased beta-phases which also evidenced by a greater fraction of light gray-scale image in back-scattered SEM analysis. The alpha phase region almost eliminated in the 35 wt% Nb. The lowest compressive strength was observed in 45 wt% Nb is due to partly crystallized region in the microstructure observed. The alloy containing 35 wt% Nb exhibited better beta-phase structures in the matrix. The Young’s modulus of 13.46±2.44 GPa were obtained from 45 wt% Nb addition in the Ti alloy. All sintered samples are potential candidates for implant applications.
Abstract: Dissimilar autogenous square butt joints between SA516Gr65 and 304L steels were produced by TIG welding and A-TIG welding with SiO2 and TiO2single component fluxes used in the as-received condition and dried at 150°C for one hour. Results showed that with A-TIG welding considerable improvement in depth of penetration could be achieved. Reversal of Marangoni convection could be the operative mechanism with the use of flux in the as-received condition while arc constriction could also contribute with the use of dried fluxes. Between the two single component fluxes viz., SiO2 and TiO2 studied SiO2 was found to be more effective in improving the depth of penetration.
Abstract: 5083 Al alloy was friction stir processed (FSP) at room temperature under various experimental conditions. Two rotational speeds of 430 and 850 rpm with a single traverse feed of 90 mm/min (430-90, 850-90) were used, to investigate the effect of rotation speed. Also, another feed rate of 140 mm/min was used with a rotational speed of 430 rpm (430-140), to investigate the effect of feed rate. The processing conditions resulted in three different grain sizes of 0.95, 1.6 and 2.6 μm depending on the FSP parameters. The deformation behavior of the FSP samples was investigated at 250 C at three strain rates of 10-4, 10-3 and 10-2 s-1. The values of strain rate sensitivity, m was determined, as a function of grain size, and it decreased from 0.45 to 0.33 to 0.18 with increasing the grain size. True activation energy was calculated as 63, 95, 157 kJ/mole for the grain sizes of 0.95, 1.6 and 2.6 μm, respectively. These calculated values are comparable to grain boundary sliding of magnesium in aluminum (69 – 78 kJ mol-1), magnesium in aluminum (~115 kJ mole-1) and aluminum lattice diffusion (~143 kJ mol-1 ). The change in the deformation mechanism with grain size was discussed in some details.
Abstract: Degradation of properties due to ageing at high temperature service is a common problem which normally occurs in electricity generation power plants, refineries, petrochemical industries. This work investigates the influence of accelerated artificial ageing on the microstructural and mechanical properties of 9-12%Cr steel usually used in power plants. This steel was tested in the as-produced and aged for 2, 5 and 8 weeks at 700°C. Results showed that the microstructural features such as phases, carbides, i.e. morphology and type, sub-grains and their boundaries and misorientation angles are the dominant factors influencing the mechanical properties. Ageing led carbides to go into solution in the martensite-ferrite structure and also led to the increase of average misorientation angle as well as to the reduction of low angle grain boundaries. In addition, ageing led to the reduction in the mechanical properties and hardness when compared to the as-produced condition.
Abstract: Tungsten heavy alloy of two different compositions (93W-4.0Ni-2.0Co-1.0Fe and 90W-6.1Ni-3.0Fe-0.5Co-0.4Mo in wt%) was synthesized in conventional powder metallurgy route through the liquid phase sintering. Studies have been carried out on the effect of alloying elements, tungsten particle size, and amount of matrix on mechanical properties. The alloy with 93% W had shown the higher tensile strength value and lower elongation along with double the value of impact energy than that of 90% W due to lower tungsten particle size and weight fraction in addition to an increase in cobalt and increase in ratio of iron to nickel. Relatively higher porosity could also have resulted in reduced properties.
Abstract: Porous metallic biomaterials produced using additive manufacturing technologies have gained popularity in orthopaedic implant applications. Porous metals provide enhanced biological anchorage for the bone tissue surrounding implants, and to promote rapid bone ingrowth. However, fragility associated with highly-porous metals is still a major concern. Standard mechanical testing yields merely structural parameters (i.e. stiffness and strength), but infers nothing about local strains in the micro-architecture such as struts. This study aims to develop a technique applicable for direct measurement of strain in porous titanium (Ti) structures. A low rigidity lattice Ti sample was specifically designed and fabricated using the Selective Laser Melting (SLM) technology. A novel compression test was performed, in which the surface lattice pattern of the Ti cube during the entire compression process was captured. Customized Matlab code was then used to compare lattice images in the unloaded and loaded states to compute strains. The results of full-field strain calculations were presented to demonstrate the capacity of the method. The characterization of localized strains from experiments can aid in the understanding of the mechanics of porous Ti structures, the relationship between microstructures and overall mechanical property, and the interpretation of failure patterns observed in complicated microstructures such as strut.
Abstract: The conditions are substantiated for the loss of thermodynamic stability of a tribosystem and for its adaptation with a decreasing wear rate at the moving frictional contact of parts from commercially pure titanium with an ultrafine-grained structure produced by equal-channel angular pressing. The regularities of the influence of the structure's dispersion degree and the friction contact's temperature on the tribotechnical characteristics of ultrafine-grained materials are established theoretically and experimentally.