Interfacial microstructure and shear strength of Ti-6Al-4V/TiAl laminate composite sheet fabricated by hot packed rolling

A two layer Ti-6Al-4V(wt%)/Ti-43Al-9V-Y(at%) laminate composite sheet with a uniform interfacial microstructure and no discernible defects at the interfaces has been prepared by hot-pack rolling, and its interfacial microstructure and shear strength were characterized. Characterization of the interfacial microstructure shows that there was an interfacial region of uniform thickness of about 250 μm which consisted of two layers: Layer I on the TiAl side which was 80 μm thick and Layer II on the Ti-6Al-4V side which was 170 μm thick. The microstructure of Layer I consisted of massive γ phases, needlelike γ phases and B2 phase matrix, while the microstructure of Layer II consisted of α₂ phase. The microstructure of the interfacial region is the result of the interdiffusion of Ti element from Ti-6Al-4V alloy layer into the TiAl alloy layer and Al element from the TiAl alloy layer into the Ti-6Al-4V alloy layer. The shear strength measurement demonstrated that the bonding strength between the TiAl alloy and Ti-6Al-4V alloy layers in the laminate composite sheet was very high. This means that the quality of the interfacial bonding between the two layers achieved by the multi-path rolling is high, and the interface between the layers is very effective in transferring loading, causing significantly improved toughness and plasticity of the TiAl/Ti-6Al-4V laminate composite sheet

Mechanical performance and fracture behavior of Fe₄₁Co₇Cr₁₅Mo₁₄Y₂C₁₅B₆ bulk metallic glass

The mechanical properties of a new Fe₄₁Co₇Cr₁₅Mo₁₄Y₂C₁₅B₆ bulk glassy alloy were studied by impact bending, compression, and hardness tests carried out at room temperature. The compressive fracture strength, elastic strain to fracture, Young’s modulus and Vickers hardness were measured to be 3.5 GPa, 1.5%, 265 GPa, and 1253 kg mm⁻², respectively. The fracture mode of the glassy alloy under uniaxial compression is different from those of other bulk metallic glasses in that this fracture mode causes the samples to be broken, in an exploding manner, into a large number of micrometer-scale pieces. The fracture mechanisms of this bulk glassy alloy under bending and uniaxial compression are discussed based on the observation of the fracture surfaces. Vickers indentation tests indicate that the structure of the glassy ingot may be inhomogeneous

Microstructure and mechanical properties of large size as-cast Ti-43Al-9V-0.2Y (at.%) alloy ingot from brim to centre

A Ti-43Al-9V-0.2Y (at.%) alloy ingot with the size of Ф160×400mm was prepared by vacuum arc remelting (VAR). The microstructure of the as-cast Ti-43Al-9V-0.2Y alloy was composed of B2/α₂/γ lamellar colonies and massive B2 and γ phases which were distributed along the boundaries of these lamellar colonies in the form of equiaxed grains. Based on the grain size variation along the radius direction of the ingot, the ingot could be divided into four ring regions from brim to centre. It has been understood that the grain size variation between these four regions was due to the interplay of the effects of the cooling rate and the yttrium content on solidified microstructures in these regions. Mechanical testing of the samples cut from these four regions showed that there existed a clear correlation between the yield strength and the average grain sizes of the four ring regions, which approximately conformed to a Hall-Petch relationship

Development and design of binder systems for titanium metal injection molding: An overview

Titanium metal injection molding (Ti-MIM) has been practiced since the late 1980s. Logically, the Ti-MIM practice follows the similar processes developed for the antecedent materials such as stainless steel and ceramics. Although Ti-MIM is a favorite research topic today, the issue of convincing the designers to use Ti injection-molded parts still exists. This is mainly because of the concern about contamination which seems unavoidable during the Ti-MIM process. Much information about the binder formulation, powder requirements, debinding, and sintering is available in the literature. There are several powder vendors and feedstock suppliers. However, most of the binders in the feedstock are proprietarily protected. The disclosed information on the binders used for formulating powder feedstock is very limited, which in turn discourages their adoption by engineering designers. This overview intends to discuss some of major binder systems for Ti-MIM available in the literature. It serves to provide a guideline for the Ti-MIM practitioners to choose a suitable powder feedstock

The mechanical behaviour of an ultrafine grained Ti-47Al-2Cr (at%) alloy in tension and compression and at different temperatures

A bulk ultrafine grained (UFG) Ti-47Al-2Cr (at%) alloy has been produced using a powder metallurgy process that combines high energy mechanical milling (HEMM) of a mixture of Ti, Al and Cr powders to produce a Ti/Al/Cr composite powder and hot isostatic pressing (HIP) of the composite powder compact. The purpose of the present study is to determine the mechanical behaviour of the alloy in tension and compression at room temperature (RT) and elevated temperatures, and also to compare the compression behaviour of the material with its tensile behaviour. It has been found that due to the residual pores, lack of full level interparticle bonding and high oxygen content (0.87wt%) in the consolidated samples, the UFG TiAl based alloy has a very low room temperature tensile fracture strength of 100 MPa and shows no tensile ductility. However these microstructural defects and high oxygen content have much less significant effect on the room temperature compressive mechanical properties, and the alloy shows a high compressive yield strength of 1410 MPa, and some ductility (plastic strain to fracture 4%). At elevated temperatures of 800oC and above, the alloy shows high tensile and compressive ductility as demonstrated by 75% tensile elongation to fracture and no cracking in upset forging with a height reduction of 50% at 900oC. The yield strength of the alloy at 900oC is 55 MPa in tension and 33 MPa in compression, both of which are lower than those of coarse grained TiAl based alloys with similar compositions at 900oC. This is due to a higher creep rate of the UFG alloy caused by the small grains. The good formability of the UFG TiAl based alloy as reflected by the lower critical temperature above which the alloy becomes highly formable indicates that the material can be used as a suitable precursor for secondary thermomechanical processing and super-plastic forming

Effect of processing condition and composition on the microhardness of Cu-(2.5-10)vol.%Al₂O₃ nanocomposite powder particles produced by high energy mechanical milling

Nanostructured Cu-(2.5-10vol.%)Al₂O₃ nanocomposites were produced using high energy mechanical milling. For the as-milled Cu- Al₂O₃ composite powder particles having Al₂O₃ volume fractions of 2.5% and 5%, the increase in average microhardness is significant with the increase of milling time from 12 hours to 24 hours. With the increase of the content of Al₂O₃ nanoparticles the microhardness increases and in the range of 255HV-270HV. The milled nanocomposite powders were heat treated at 150, 300, 400 and 500°C for 1 hour, respectively, to determine the thermal stability of the powder particles as a function of annealing temperature. The average microhardness increased/decreased for the Cu- Al₂O₃ composites after annealing at 150°C due to the dislocation density, while increasing the annealing temperature to 300°C and 400°C the average microhardness almost remained mostly unchanged. Further increasing the annealing temperature to 500°C causes significant decrease in average microhardness due to reduction in dislocation density and coarsening of Cu grains of the Cu- Al₂O₃ composite powders produced after 24 hours of milling. This paper is to report and discuss the changes of the microhardness of the material, caused by the compositions and processing conditions, used to fabricate the Cu-(2.5-10)vol.% Al₂O₃ nanocomposite powders