Theoretical investigations of half-metallic ferromagnetism in new Half-Heusler YCrSb and YMnSb alloys using first-principle calculations

Structural,electronic,and magnetic properties of new predicted half-Heusler YCrSb and YMnSb compounds within the ordered MgAgAs Clb-type structure are investigated by employing first-principal calculations based on density functional theory.Through the calculated total energies of three possible atomic placements,we find the most stable structures regarding YCrSb and YMnSb materials,where Y,Cr(Mn),and Sb atoms occupy the(0.5,0.5,0.5),(0.25,0.25,0.25),and(0,0,0) positions,respectively.Furthermore,structural properties are explored for the non-magnetic and ferromagnetic and anti-ferromagnetic states and it is found that both materials prefer ferromagnetic states.The electronic band structure shows that YCrSb has a direct band gap of 0.78 eV while YMnSb has an indirect band gap of 0.40 eV in the majority spin channel.Our findings show that YCrSb and YMnSb materials exhibit half-metallic characteristics at their optimized lattice constants of 6.67 and 6.56 ,respectively.The half-metallicities associated with YCrSb and YMnSb are found to be robust under large in-plane strains which make them potential contenders for spintronic applications.

Wettability of Monocrystalline Silicon Carbide by Molten Metals and Binary Metal－Silicon Alloys

The wettability of monocrystalline silicon carbide by liquid metals (Au , Ge, Ag , Sn and Cu) and binarymetal-silicon (Ag-Si and Sn-Si) alloys was investigated between their melting points and 1430℃ with the ses-sile drop method in argon with an extremely low oxygen partial pressure. For Au and Ge on SiC, the contactangles exhibited a weak temperature dependence. Under the same experimental conditions, however, complexwetting behaviours were observed for Ag , Sn and Cu on SiC , which could be attributed to the chemical reactivi-ties between the metals and the ceramic.Additional experirnents were also performed for binary Ag-Si and Sn-Si alloys on the same SiC substratesunder the same experimental conditions. The obtained coiitact angle isotherms for the two binary alloy/SiC sys-tems were discussed and interpreted by using a statistical thermedynamics mixlel.

TRANSIENT TEMPERATURE FIELDS AND RESIDUAL STRESS FIELDS OF METALLIC MATERIALS UNDER WELDING

Based on the situation of welding thermal conduction and thermo-elasto-platicity research, this paper explores some problems in this field. First, the boundary element method for nonlinear problems is improved by linearization of nonlinear problems and used in welding thermal conduction analysis. Second, the thermo-elasto-plastic finite element method is used for the welding stress calculation, in which the phase transformation is considered by the 'equivalent linear expansion coefficient method'. The comparison of the calculated results with experimental data shows that the methods provided in this paper are available.

Extending the Lifetime of Copper-beryllium Alloys as Plastic Injection High-end Needle Valve Mold Nozzle Tips Through a Heat-treatment-based Microstructure Optimization Approach

The relationship between the microstructure and the practical performance of two different copper-beryllium alloys including their lifetime has been investigated.Herein,two valves made of two different alloys with very similar compositions and the same heat treatment methods were investigated by various standard techniques including metallography,X-ray diffraction,chemical composition,microhardness,and thermal conductivity measurements.Although both alloys experienced the same heat-treatment processes,they revealed different thermal and mechanical properties due to the minor difference in their chemical composition.The alloy providing a longer lifetime (40%more) as the tip had a higher thermal conductivity of 280.3 W(m·K)^(-1) (about two times that of the other alloy).Regarding the metallography images and the measured thermal conductivity values of the alloys,the extended lifetime of the nozzle with the optimum performance is ascribed to its biphasic microstructure and the minor grain boundaries and interfacial thermal resistance.And important difference in the chemical composition was investigated in this study.

A new post-weld heat treatment to improve toughness of 9Cr-1Mo steel weld metals

9Cr-1Mo ferritic steels have been used in the conventional power generation plants due to their excellent creep resistance. However, one of the main obstacles in welding 9Cr-1Mo steels is the formation of undesirable coarse columnar grains in weld metal whieh ean severely compromise the toughness. A new post-weld heat treatment （PWHT） is developed in the present work. Unlike the conventional processes in which the post-weld heat treatment is carried out below Ac1 , the use of temperatures above the Ac1 of 9Cr-1Mo alloy is considered. The new PWHT at a temperature above Ac1 improves the toughness of 9Cr-1Mo weld metals effectively. The improvement in toughness is mainly due to refinement and homogenization of mierostruetures. Key words

Interfacial structure and mechanical property of Al2O3 and Invar brazed joint

This paper introduces a brazing process between Al2O3 ceramic and Invar alloy.Al2O3 can be brazed with Invar effectively.The interfacial structure of Al2O3/Invar joint can be expressed as：Invar/Ag（s,s）＋Cu（s,s）＋Fe2Ti（zone Ⅰ）/Ag（s,s）＋Cu（s,s）＋Fe2Ti＋NiTi＋Cu3Ti（zone Ⅱ）/Ag（s,s）＋Cu（s,s）＋Cu2Ti＋Al（s,s）＋TiC＋TiO（zone Ⅲ）/Al2O3.The maximum shear strength of 139 MPa was measured for as-brazed Al2O3/Invar joint brazed at 850℃ for 25 min or 900℃ for 15 min.

Effect of multiaxial deformation on structure, mechanical properties, and corrosion resistance of a Mg-Ca alloy

This article provides a report on the effect of multiaxial deformation(MAD) on the structure, texture, mechanical characteristics, and corrosion resistance of the Mg-0.8(wt.)% Ca alloy. MAD was carried out on the alloy in the as-cast and the annealed states in multiple passes, with a stepwise decrease in the deformation temperature from 450 to 250 ℃ in 50 ℃ steps. The cumulative true strain at the end of the process was 22.5. In the case of the as-cast alloy, this resulted in a refined microstructure characterized by an average grain size of 2.7 μm and a fraction of high-angle boundaries(HABs) of 57.6%. The corresponding values for the annealed alloy were 2.1 μm and 68.2%. The predominant mechanism of structure formation was associated with discontinuous and continuous dynamic recrystallization acting in concert. MAD was also shown to lead to the formation of a rather sharp prismatic texture in the as-cast alloy, whilst in the case of the annealed one the texture was weakened. A displacement of the basal poles {00.4} from the periphery to the center of a pole figure was observed. These changes in the microstructure and texture gave rise to a significant improvement of the mechanical characteristics of the alloy. This included an increase of the ultimate tensile strength reaching 308 MPa for annealed material and 264 MPa for the as-cast one in conjunction with a twofold increase in ductility. A further important result of the MAD processing was a reduction of the rate of electrochemical corrosion, as indicated by a significant decrease in the corrosion current density in both microstructural states of the alloy studied.

INFLUENCE OF PLATE THICKNESS ON FATIGUE BEHAVIOUR OF WELDED JOINTS IN AIR AND IN SEA WATER

Bending fatigue tests were carried out on cruciform welded joints of China-made platform steel E36-Z35 with plate thickness of 16mm, 32mm and 40mm. The tests consisted of testing in air and in sea water with and without cathodic protection (-850mV. SCE). The sea water corrosion fatigue tests were conducted at loading frequency of 0.2 Hz and sea water temperature of 20°C. The test results show an obvious reduction in fatigue strength of welded joints with increasing plate thickness in all the three test conditions. The present paper proposes different thickness corrections for fatigue strength and fatigue life of welded joints in air and in sea water with and without cathodic protection respectively. In addition, an explanation for thickness effect on fatigue life of welded joints is given by using the theory of fracture mechanics.

TEM Morphology and FCP Rate of Ti-5Al-2Mo-3Zr Alloy

The transmission electron microscopic morphology of the phases and fatigue crack propagation (FCP) rate of Ti-5Al-2Mo-3Zr alloy were investigated in this study. Microstructure of the alloy consists of α and β phases after furnace- and air-cooling, and interfacial phase appears at the boundaries between these two phases. After water quenching, the microstructure consists primary of α and h.c.p. martensite α′ which assumes acicular. There are many twins within the α′ plates. No retained β phase exists after quenching from any temperature. During aging, β particles precipitated along the boundaries and inside the martensite plates with Burgers orientation relationship. The fatigue crack propagation rate (low frequency) is not sensitive to the microstructure, tensile strength and rolling direction. Analysis of the fractography shows that main cracks propagated serpentinely and secondary cracks existed everywhere. In high stress intensity range, the resistance of FCP is better than that of Ti-6Al-4V.

Effect of ECAP on the Microstructure and Mechanical Properties of a High-Mg_2Si Content Al-Mg-Si Alloy

A high-Mg2Si content Al alloy was extruded by equal channel angular pressing（ECAP） for 8 passes at 250 ℃ and an ultrafine-grained structure with an average grain size of about 1.5 μm was achieved.The coarse skeleton-shaped Mg2Si phase presenting in the as-cast alloy are significantly fragmented into fine rod-shaped as well as equiaxed particles mostly less than about 230 nm and become relatively dispersed.The tensile strength 192.8 MPa and the elongation up to 31.3% at ambient temperature are attained in the 8-pass ECAPed alloy versus 163.3 MPa and 9.1% in the as-cast alloy.High-temperature creep test at 250 ℃ reveals that the ECAPed sample exhibits a high elongation close to 100% at a relatively high creep rate 7.64×10-5 s-1,compared to the elongation 56% at a low strain rate 1.74×10-7 s-1 in the as-cast alloy.

Mechanical Property and Microstructure of Oxide Dispersion Strengthened Nickel-base Superalloy MA758

The mechanical property and microstructure of a mechanically alloyed (MA) oxide dispersion strengthened (ODS) nickel base superalloy MA758 were investigated by compression testing and microscopy techniques. It was found that the yield strength of the as extruded fine grain material is significantly dependent on temperature, droping from 880 MPa at 560℃ down to 15 MPa at 1160℃. The yield strain also drops with temperature, from 0.037 at 560℃ to 0.024 at 1160℃. The second part of the current research has revealed large amount of strings of Al 2O 3 particles forming after high temperature annealing in air, aligned along the extrusion direction. Upon annealing in vacuum, such particles do not formed, though Ti/Cr nitrides and carbides are present in small quantities. This phenomenon explains the observed weak transverse mechanical property in several ODS alloys.

Structural, elastic, phonon and electronic properties of a MnPd alloy

The structural, elastic, phonon and electronic properties of a MnPd alloy have been investigated using the first- principles calculation. The calculated lattice constants and electronic structure agree well with the experimental results. The microscopic mechanism of the diffusionless martensitic transition from the paramagnetic B2 （PM-B2） phase to the antiferromagnetic L10 （AFM-L10） phase through the intermediate paramagnetic L10 （PM-L10） phase has been explored theoretically. The obtained negative shear modulus C＇ - （C11 - C12）/2 of the PM-B2 phase is closely related to the instability of the cubic B2 phase with respect to the tetragonal distortions. The calculated phonon dispersions for the PM-L10 and AFM-L10 phases indicate that they are dynamically stable. However, the AFM-L10 phase is energetically most favorable according to the calculated total energy order, so the PM-L10 -＋AFM-L10 transition is caused by the magnetism rather than the electron-phonon interaction. Additionally, the AFM-L10 state is stabilized through the formation of a pseudo gap located at the Fermi level. The calculated results show that the CuAu-I type structure in the collinear antiferromagnetic state is dynamically and mechanically stable, thus is the low temperature phase.

Mechanical Property and Microstructure of Oxide Dispersion Strengthened Nickel－base Superalloy MA758

The mechanical property and microstructure of a mechanically alloyed ( MA) oxide dispersionstrengthened (ODS) nickel-base superalloy MA758 have been investigated by compresion testing and mi-croscopy techniques. The yield strength of the as-extruded fine grain material is extremely significantly de-pendent on temperature, dropping from 880 MPa at 560℃ down to 15 MPa at 1160℃. The yield attain also drops with temperature, from 0. 037 at 560℃ to 0. 024 at 1160℃. The second part of the current research has revealed large amount of strap of Al_2O_3 particles forming after high temperature annealing inair, aligned along the extrusion direction. Upon annealing in vacuum, such particles do not form, thoughTi/Cr nitrides and carbides are present in small quantities. This phenomenon explains the hoed weaktransverse mechanical property in several ODS alloys.

A Noveland Simple Creep Testing Method and Its Use in Measuring the Creep of Solder

A simple creep testing method is presented which involves using coiled specimens. With this method, a single experiment can give all the data required for a plot of strain rate versus stress. The value of the stress-expo-nent of room temperature steady-state creep a Pb-61. 5wt %Sn solder was measured in this way to be 1. 06,aselected from a diffusion creep mechanism.

Stress－rupture Property and Microstructure of Yttria Dispersion Strengthened Alloy MA956

The streas-rupture property and corresponding deformed microstructures of an yttria dispersionstrengthened alloy bar MA956 ( Fe-20 % , Cr-4. 5 % , Al-0. 5% , Ti-0. 5% , Y_2O_3(wt% ) ) were investi-gated by using tensile stress-rupture testing, fractography (optical and scanning electron micrscopy(SEM)) , and optical metallography. It has been found that the longitudinal strength is much higher thanthe transverse strength, as a result of fracture occurring along grain boundaries in the latter orientationwhen the load direction is normal to the recrystallization grain growth direction. For the same reason, lon-gitudinally tested samples fractured in a ductile manner while transversely tested ones had brittle fracture.It is also found that pre-anneal decreases the longitudinal strength, since it reduces the grin size and there-fore increace the amount of grain boundarings. In addition, the effect of grain size on crack propagation wasexamined .

Researches on Ni-P Alloys

Worldwide researches on Ni-P alloys have been briefly reviewed,including their corrosion resistance, crystallisation behaviour,amorphisation by ion implantation,and usage as underlayer for thin film magnet- ic media.

Antibacterial metals and alloys for potential biomedical implants

Metals and alloys,including stainless steel,titanium and its alloys,cobalt alloys,and other metals and alloys have been widely used clinically as implant materials,but implant-related infection or inflammation is still one of the main causes of implantation failure.The bacterial infection or inflammation that seriously threatens human health has already become a worldwide complaint.Antibacterial metals and alloys recently have attracted wide attention for their long-term stable antibacterial ability,good mechanical properties and good biocompatibility in vitro and in vivo.In this review,common antibacterial alloying elements,antibacterial standards and testing methods were introduced.Recent developments in the design and manufacturing of antibacterial metal alloys containing various antibacterial agents were described in detail,including antibacterial stainless steel,antibacterial titanium alloy,antibacterial zinc and alloy,antibacterial magnesium and alloy,antibacterial cobalt alloy,and other antibacterial metals and alloys.Researches on the antibacterial properties,mechanical properties,corrosion resistance and biocompatibility of antibacterial metals and alloys have been summarized in detail for the first time.It is hoped that this review could help researchers understand the development of antibacterial alloys in a timely manner,thereby could promote the development of antibacterial metal alloys and the clinical application.

A universal function of creep rate

In this paper, we derive a universal function from a model based on statistical mechanics developed recently, and show that the function is well fitted to all the available experimental data which cannot be described by any function previously established. With the function predicting creep rate, it is unnecessary to consider which creep mechanism dominates the process, but only perform several experiments to determine the three constants in the function. It is expected that the new function would be widely used in industry in the future.