Band 108, Heft 5

Quality, performance, reliability, cost etc. of any product are all affected by the material being used to manufacture it. Hence, it becomes imperative to select an appropriate material for a successful product. Material selection involves a complex interaction between component function, material type, process, shape and cost. The designer must have a broad understanding of various properties of materials and their processing characteristics. No two materials have the same properties, and the choice is usually decided by the best possible combination of material properties and economic factors providing an optimal solution. In this paper, the best suited materials for two products, i. e. engine flywheel and metallic gear, are selected applying an almost unexplored multi-criteria decision making tool in the form of the TODIM (TOmada de Decisao Interativa Multicriterio, which means in Portuguese “interactive and multi-criteria decision making”) method. The derived results corroborate those obtained by past researchers. A sensitivity analysis showing the effect of varying values of attenuation factor of the losses on the rankings of the candidate materials proves the robustness and applicability of the TODIM method in solving material selection problems. Finite element analysis is carried out to study the behavior of the candidate materials under specific loading conditions.

A combinatorial approach has been applied to build the database of composition dependent microstructure and hardness of the Ti5553–Fe system. The relationship between the composition and microstructure as well as the hardness was obtained. (Ti5553) 96 -Fe 4 was found to have almost the same hardness as that of Ti5553, but a relatively coarser intragranular α phase. High-angle annular dark field imaging revealed that Fe mainly concentrated in the β phase, which strengthened the β phase through solution strengthening. This means that (Ti5553) 96 -Fe 4 may have the same strength as that of Ti5553 but higher fracture toughness. The formation of FeCr compound consumed the β stabilizer elements Fe and Cr, which led to unusual increasing of the nucleation rate and the volume fraction of α phase in (Ti5553) 88 -Fe 12 .

In this study, the evolutions of the microstructures and microsegregation are related to the cooling curve in equiaxed dendritic solidification of the Al-5 wt.% Cu alloy. In addition to regular branching of dendritic arms, leaf venation branching, free branching and radial branching were also observed. With the extension of the dendritic zone, both the composition of the extra-dendritic melt and average composition of the dendritic zone change. The microsegregation mechanism in the dendritic zone deviates from the modified Scheil model. The microsegregation data suggest that the single dendritic arm is a porous structure containing the trapped boundary layer. As the temperature decreased after the isothermal periods, some original dendritic arms and interdendritic melt converged to form a new dendritic arm.

In this paper, materials in the Ir–Ru–B system with nominal compositions of Ir–Ru–2B and 3Ir–Ru–4B were synthesized by arc melting and vacuum hot press (VHP) sintering. The phase composition and microstructure were characterized using X-ray diffraction, back scatter electron imaging, energy dispersive spectroscopy and electron back scatter diffraction. Different preparation processes for these Ir–Ru–B system materials were studied. The results show that Ir–Ru–2B prepared by arc melting and VHP sintering contains Ir(Ru)B 0.9 and Ru(Ir)B solid solutions, while 3Ir–Ru–4B contains Ir(Ru)B 0.9 , Ru(Ir)B 2 and Ir(Ru) solid solutions. The error for the lattice parameters of the VHP sintered samples was larger than that of the arc melted samples. The energy spectrum analysis of the Ir–Ru–2B samples prepared using different processes indicates that the solubility of the solid solutions in the VHP sintered samples was higher than the solubility in the arc melted samples. The formation mechanisms for the (Ir, Ru)–B, (Ir(Ru)B 0.9 , Ru(Ir)B 2 and Ru(Ir)B) and Ir(Ru) solid solutions are discussed in detail. There is more Ir(Ru) solid solution in the VHP sintered sample than in the arc melted sample, and the grain orientation of the former is more complex than that of the latter.

Alumina matrix ceramic composites toughened by AlTiC master alloys, diopside and rare earths were fabricated by hot-pressing and their thermal shock behavior was investigated and compared with that of monolithic alumina. Results showed that the critical thermal shock temperature (Δ T ) of monolithic alumina was 400 °C. However, it decreased to 300 °C for alumina incorporating only AlTiC master alloys, and increased with further addition of diopside and rare earths. Improvement of thermal shock resistance was obtained for alumina ceramic composites containing 9.5 wt.% AlTiC master alloys and 0.5 wt.% rare earth additions, which was mainly attributed to the formation of elongated grains in the composites.

This study examined the effects of addition of alumina nanoparticles on the microstructure, tribological and corrosion properties of CuTi alloy. Mechanical alloying was performed employing satellite ball milling. X-ray diffraction revealed that CuTi solid solution was formed after 40 h of mechanical alloying. Mechanically alloyed powder was cold-pressed and sintered at 850 °C. Alumina nanoparticles were uniformly dispersed in the CuTi alloy matrix. Tribological properties of the samples were evaluated by pin-on-disk wear testing. The results showed a decrease in wear rate by 30 % owing to the presence of nanoparticles in the nanocomposite. The corrosion properties of samples were assessed employing potentiodynamic polarization and immersion methods in a 3.5 wt.% NaCl solution. The corrosion current density of CuTi alloy decreased from 125.9 to 6.3 μA · cm −2 following the addition of alumina nanoparticles.

Austenitic stainless steels are often used to handle organic acids such as acetic acid (CH 3 COOH), which are extensively used in food contact applications and chemical industries for manufacturing medicines, nutrition and various chemical amalgams. In the present investigation an attempt has been made to compare the corrosion behavior of Cr–Ni (AISI type 304), Cr–Mn–Ni (type 201) and Cr (type 430) stainless steel for economical replacement of higher cost Cr–Ni grade. Immersion testing was performed at room temperature and boiling temperature in acetic acid. Atomic absorption spectroscopy was carried out to evaluate metal ion concentration in the immersion solution. The surface morphology of pit formation was characterized using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The effect of elemental leaching on electrical conductivity of the immersion solution was evaluated and correlated with pH measurements. A new mechanism has been proposed for the pit formation due to manganese sulfide inclusions. The replacement compatibility was further confirmed with anodic polarization testing and a successful replacement was established for room temperature applications.

Electron beam welding was employed on Ti-6Al-4V ELI alloy with 50 mm thickness. The weld morphologies were I and T shape, respectively with and without oscillation. The microhardness profiles and tensile properties of the welds were measured along the penetration, and the mis-match was investigated. The maximum microhardness was in the welds and was at least 1.06 times that of the base metal. In addition, the hardness distribution of the I shape weld was more homogeneous than that of the T shape. The tensile strengths of the welds were higher than the base metal, and the properties of the I shape weld were more homogeneous. The mis-match factors of the welds were above 1.0, and the strengths of the joints were equivalent to the base metal, which verified the overmatching. The microstructure and hardness difference resulted in inhomogeneous stress–strain behavior of the joint, which contributed to the overmatching.

With an increase in the addition of W, the morphology and volume percentage of Fe 2 B show no obvious variation. Although an increase in the hardness of the alloy has a beneficial effect on improving wear resistance, toughening Fe 2 B by the addition of W has a more helpful role in the wear resistance of Fe–B–C alloy in this study. The weight loss of Fe–B–C alloy with the addition of 2.04 wt.% W can be decreased by more than 47 % of that of the alloy without added W.

The thermal stability of Al- RE (rare earth) intermetallic phases with individual RE for heat-resistant high-pressure die-casting Mg–Al– RE alloys is investigated. The results of this study show that the main strengthening phase of Mg-4Al-4Ce alloy is Al 11 Ce 3 , whose content is about 5 wt.% according to quantitative X-ray diffraction phase analysis. The Al 11 Ce 3 phase appears to have high thermal stability at 200 °C and 300 °C, while phase morphology change with no phase structure transition could occur for Al 11 Ce 3 when the temperature reaches 400 °C. Furthermore, besides the kinds of rare earths and temperature, stress is also an influencing factor in the microstructural stability of Mg-4Al-4Ce alloy.