Effect of Substrate Characteristics on Interdiffusion Coefficients of Ni and Al Atoms inβ-NiAl Phase of Aluminide Coatings

Interdiffusion coefficients at 950℃ and 1050℃ are calculated by Wagner analysis method as a function of composition of β-NiAI phase. Theβ-NiAI phase is formed by pack cementation on surface of superalloy. Results of the calculation show that interdiffusion coefficients inβ-NiAI phase strongly depend on the compositions and vary over several orders of magnitude. Compared with the interdiffusion coefficients in the stoichiometricβ-NiAI phase, the interdiffusion coefficients in β-NiAI phase formed on superalloy is obviously small, probably due to the composition, complicated microstructure and precipitates. However, it could be seen clearly that the shapes of the diffusivity curves are very similar to each other. The similarity of the diffusion curves and the difference between interdiffusion coefficients imply that the compositions, microstructures and precipitates of superalloy have a distinctly adverse effect on the interdiffusion of Ni and Al atoms during aluminization, but do not change the essential characteristics of β-NiAI phase.     

Effect of Al Content on Precipitation of α_2 Ordered Phase in Ti-Al-Sn-Zr-Mo-Si-Nd Alloys

The precipitation characteristics of the α2 ordered phase in Ti-AI-Sn-Zr-Mo-Si-Nd alloys with various content of Al, under different aging conditions, were investigated. The distribution and size of the α2 ordered phase changed with temperature and Al content. The dislocations were the only places where the α2 ordered phase could precipitate at higher temperature near the critical transformation temperature for each alloy experimented. With the addition of Al content, the critical transformation temperature of α2 ordered phase increased. When the aging temperature was relatively low (650℃), the precedent precipitation of α2 ordered phase took place in primary a phase at the early stage of aging, in the duplex microstructure (the primary a with the transformed (3) of the alloys with lower Al content. But after certain aging time (50 h), the size of α2 particles was almost equal in both the primary a and the transformed β. And no obvious growth of α2 particles could be observed after 50 h.     

Influence of α Phase on Shape Memory Effect and Superelasticity of CuZnAI Alloy

The influence of a small amount of α phase inβ′ matrix on shape memory effect andsuperelasticity of CuZnAl shape memory alloy hasbeen studied systematically.It has been found thattransformation temperature can be adjusted in alarge scale by controlling the amount of α phase,meanwhile,shape memory effect and superelasticitydo not decrease obviously when there exists a smallamount of α phase.Based on the optical and trans-mission electron microscopy observation,the influ-ence of α phase on shape memory effect andsuperelasticity has been discussed.     

Effect of the Eutectic Phase on the Microstructure and Tensile Strength of an Al–Zn–Ni–Mg–Cu Casting Aluminum Alloy

Strength of Materials - The effect of composition, casting, and heat treatment on the eutectic phase morphology of an Al–Zn–Ni–Mg–Cu casting aluminum alloy was studied. The...     

Effect of upset forging on microstructure and tensile properties in a devitrified Al–Ni–Co–Y Alloy

Devitrified Al—transition metal—rare earth alloys offer routes to obtain higher volume fractions of dispersed strengthening phases than conventional precipitation routes. Here, we report a study of the microstructure–property relationships of an Al–Ni–Co–Y alloy processed by gas atomization and consolidated/devitrified by warm extrusion. Microstructural characterization by electron microscopy and serial section FIB tomography show that the alloy comprises an FCC Al matrix and 44 % by volume of elongated Al₁₉(Ni,Co)₅Y₃ plates with the Al₁₉Ni₅Gd₃ structure. The plates are aligned with the extrusion direction in the as-extruded alloy, and tensile data show a distinct anisotropy in yield strength and strain to failure. These data are consistent with the alloy acting more like a unidirectional short-fiber-reinforced metal–matrix composite than a conventional precipitation-hardened alloy. During axial upset forging, the ternary plates do not break up, but instead they rotate, until at large upset strains they lie perpendicular to their original orientation with corresponding changes in the tensile properties. The materials exhibit yield strengths of up to 713 MPa and tensile elongations of up to 5 %. Thus, such systems could form the basis for truly deformable high-strength low-density metal–matrix composites.     

Effect of Cu content on microstructure and mechanical properties of in-situ β phases reinforced Ti/Zr-based bulk metallic glass matrix composite by selective laser melting(SLM)

In this study,non-toxic in-situβphases of reinforced Ti/Zr-based bulk metallic glass matrix composites(BMGCs)of(Ti_0.65Zr_0.35)100-xCux(x=5,10,15 at.%)are fabricated via selective laser melting.The effect of Cu content on phase formation,microstructure,and mechanical properties is investigated.The average volume fraction and width of theβphase decreases with increasing Cu content,while a more amorphous phase and the(Ti,Zr)₂Cu phase forms.In the center zone of the molten pool,theβphase grows in the direction of the temperature gradient,and the amorphous phase distributes among theβphases.This occurs using:sphere morphology(for x=5),a more continuous elongated sphere and network morphology(for x=10),and network morphology(for x=15),respectively.In the edge zone of the molten pool,due to the smaller cooling rate and the existence of a partially molten zone,theβphase becomes coarser,and an amorphous phase forms for more continuous networks.Furthermore,the hardness improves significantly with increasing Cu content.No crack is found for x=5.Although the average volume fraction of theβphase for x=5 is about 90%,the compression yield strength is 1386±64 MPa,reaching to an average level of conventionally fabricated counterparts,due to finer microstructure,and twinning and martensitic transformation of theβphase.