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The γ/γ' microstructure is a key factor for the mechanical performance of nickel-based single crystal superalloys. Experimental results have shown that the size and shape of the γ' precipitates are not uniform and follow certain probability distributions. In order to study the effect of the microstructure on the mechanical behavior of the superalloys, a method is proposed to reproduce its initial microstructure with the distribution function of its γ′ particle size. The effect of different microstructures on the creep behavior at different locations of a real blade is predicted to demonstrate the application of the method. It can be found from the simulation results that the mechanical behavior of the blade is related to not only the thickness of the blade wall but also the position in the blade. [ABSTRACT FROM AUTHOR]

Abstract: Except for the recoverable strain induced by phase transformation, NiTi alloys are very ductile even in the martensite phase. The purpose of the present paper is to study the influence of permanent deformation, which results from plastic deformation of martensite, on the mechanical behaviour of pseudoelastic NiTi alloys. Based on phenomenological theory of martensitic transformation and crystal plasticity, a new three dimensional micromechanical model is proposed by coupling both the slip and twinning deformation mechanisms. The present model is implemented as User MATerial subroutine (UMAT) into ABAQUS/Standard to study the influences of plastic deformation on the stress and strain fields, and on the evolution of martensite transformation. Results show that with the increasing of plastic deformation the residual strain increases and the phase transformation stress–strain curves from the martensite to austenite become steeper and less obvious. Both characteristics, stabilisation of martensite and impedance of the reverse transformation, due to plastic deformation are captured. [Copyright &y& Elsevier]

Abstract: Ti–Zr–Cu–Pd–Sn bulk glassy alloys have been synthesized by copper mold casting. The thermal properties, glass-forming ability (GFA) and mechanical properties were examined by differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffractometry (XRD) and compression test. The series of bulk glassy alloys is expected to be used as biomedical materials because of the absence of toxic elements such as Ni, Al and Be. The 10mm rods with full glassy structure can be obtained for the Ti40Zr10Cu34Pd14Sn2 and Ti40Zr10Cu32Pd14Sn4 alloys by copper mold casting. The Ti40Zr10Cu36−x Pd14Sn x (x =0, 2, 4, 6) glassy alloys have a large supercooled liquid region of over 50K. The Ti40Zr10Cu34Pd14Sn2 bulk glassy alloy exhibits good plasticity of 3.5% during compressive applied load at ambient temperature in conjunction with distinct yield strain of 2.2% and high fracture strength of about 2050MPa. [Copyright &y& Elsevier]

Abstract: (Ti40Zr10Cu36Pd14)100−x Nb x (x =1, 3, 5at.%) bulk metallic glasses containing nano-particles exhibited ultrahigh strength and distinct plastic strain. The yield strength exceeding 2050MPa, Young''s modulus of about 80GPa and the plastic strain of over 6.5% were obtained for 1% and 3% Nb-added alloys due to the suppression of the propagation of shear bands by nano-particles in situ formed in the glassy matrix. The developed Ni-free Ti-based bulk metallic glasses with low Young''s modulus and good mechanical properties are promising candidates for application as artificial dental root materials and other biomaterials. [Copyright &y& Elsevier]

Abstract: A Ti coating has been deposited on Zr55Al10Ni5Cu30 bulk metallic glass (BMG) by DC magnetron sputtering method. The formation of bone-like apatite on Ti-coated Zr55Al10Ni5Cu30 BMG was studied in this paper. Scanning electron microscopy (SEM) was used to observe the surface morphology of Ti-coated Zr55Al10Ni5Cu30 BMG and Zr55Al10Ni5Cu30 BMG after alkali treatment and immersion in Hanks'' solution. X-ray photoelectron spectroscopy (XPS) was applied to obtain the constituents information of the treated samples. A bone-like apatite layer was formed on Ti-coated Zr55Al10Ni5Cu30 BMG after immersion in Hanks'' solution with previous treatment in 5M NaOH solution. [Copyright &y& Elsevier]

Abstract: The crystallization behavior and mechanical properties of Ti40Zr10Cu36Pd14 bulk metallic glass were investigated. Nano-composites consisting of glassy matrix are formed in the alloys annealed at 693 and 723K. After annealing at 823K, the residual glass is completely crystallized. High yield strength of over 2100MPa and distinct plastic strain of 0.8% are obtained in the nano-composite alloy annealed at 693K. The compressive strength decreases for the alloys annealed at higher temperatures of 723 and 823K, accompanying with the progress of crystallization. The alloy rods both in as-cast and annealed (at 693K for 10min) states show the fracture surfaces consisting of vein pattern. On the other hand, the fracture morphology of the alloys annealed at 723 and 823K changes to brittle character with flat facets. [Copyright &y& Elsevier]

Abstract: In this paper, a finite element method (FEM) has been applied to predict the pseudoelastic behavior of NiTi shape memory alloys at different temperatures with only one temperature testing results. A three-dimensional micromechanical model has been developed based on Gall and Lim’s expression for Gibbs free energy. The difference of elastic properties between austenite and martensite are taken into consideration. The formulations for the evolution of volume fraction of the 24 martensite variants are derived. The time-discrete evolutionary equations are presented with the expression of the mechanical Jacobian matrix. This model has been implemented as UMAT into ABAQUS, which is used to simulate the pseudoelastic behavior by aggregate grains. The grain number in the aggregate is big enough to have little influence of the grain number on the simulated behavior. Tensile experiments are performed at 28, 35 and 50°C. The experimental results at 35°C are used to validate the pseudoelastic model and derive the model parameters, which are used to predict the pseudoelastic behavior at 28 and 50°C. Two kinds of predictions are presented. One considers different elastic modulus at different temperatures. And the other uses the same elastic modulus at different temperatures. Both show satisfactory agreement with the experimental results. [Copyright &y& Elsevier]

Abstract: In the present work, a three-dimensional micromechanical model has been developed based on Gall and Lim''s expression for Gibbs free energy, which can reproduce the pseudoelastic behavior of NiTi shape memory alloys. The emphasis was put on the difference of elastic properties between austenite and martensite. The formulations for the evolution of volume fraction of the 24 martensite variants are derived. The discrete evolutionary equations are presented, with the expression of the mechanical Jacobian matrix. The model is implemented as User Material subroutine (UMAT) into ABAQUS. The model formulations and finite element method (UMAT) have been validated by numerical method. As an example, pseudoelastic response of a polycrystal NiTi shape memory alloy under uniaxial loading has been simulated. The distributions of the martensite and Mises stress are quite uniform. The Mises stresses are higher during loading than unloading, while the volume fractions during loading are lower than that during unloading at the same strain level. The results show that the model can predict experiments better than that without considering different elastic properties between austenite and martensite. [Copyright &y& Elsevier]

Abstract: In the present study we use finite element stress and strain analysis to study the stress induced martensitic transformations near the crack tip of compact tension (CT) specimens of pseudoelastic NiTi shape memory alloys. For this purpose, Aurichio''s model for pseudoelasticity was implemented into the finite element code ABAQUS. The material parameters required in the model were adjusted according to loading/unloading data from pull–pull tests on pseudoelastic NiTi wires. Stress induced martensite forms near the notch of a CT specimen with no pre-crack. The presence of a sharp pre-crack alters the results considerably. The results presented in this paper provide some guidance for the interpretation of fracture mechanics tests on pseudoelastic shape memory alloys. [Copyright &y& Elsevier]

Abstract: This paper reviews our recent results on the developments and applications of the following four kinds of advanced materials having unique elastic properties in the absence of poisonous and allergic elements, i.e. (1) nanocrystalline Ti-based alloys with low Young''s modulus, high tensile strength and high corrosion resistance, (2) new super-elastic Ti-based alloys with a large elastic strain up to 4% and high tensile strength, (3) new Pd-based bulk glassy alloy with a very low critical cooling rate of about 1K/s, and (4) porous glassy Pd-based alloys with low Young''s modulus, large plastic strain and high absorption energy up to failure. These promising properties caused by unique alloy designs and material morphology indicate the possibility that the newly developed advanced alloys are used in various engineering fields including biomedical materials. [Copyright &y& Elsevier]

Abstract: A newly designed (Cu0.6Hf0.25Ti0.15)90Nb10 bulk metallic glass (BMG) composite with an excellent combination of high corrosion resistance and superior mechanical properties was successfully synthesized. The micrometer-sized ductile Nb-rich dendrite phase disperses homogeneously in the glassy matrix. Addition of Nb to the Cu–Hf–Ti alloy results in a significant decrease in the corrosion rates in the solutions examined. The high corrosion resistance of the (Cu0.6Hf0.25Ti0.15)90Nb10 BMG composite is attributed to the formation of Hf-, Ti-, and Nb-enriched highly protective surface films during immersion in acid- and chloride-ion-containing solutions. The composite alloy exhibits a high compressive true yield strength of 2073MPa and true fracture strength of 2232MPa together with a large true plastic strain of 14.1%. The embedded micrometer-sized dendrites in the glassy matrix retard inhomogeneous shear deformation and contribute to the large plastic strain. [Copyright &y& Elsevier]