Preparation and properties of W–Cu–Zn alloy with low W–W contiguity

The W–Cu–Zn alloy with a-brass matrix and low W–W contiguity was prepared by method of electroless copper plating combined with spark plasma sintering(SPS) method.The effects of process and parameters on the microstructure and mechanical properties of the alloy were investigated.The W–Cu–Zn alloy with a relative density of 96 % and a W–W contiguity of about 10 % was prepared by original fine tungsten particles combined with wet mixing method and SPS solid-state sintering method at 800 °C for 10 min.The microstructure analysis shows that Cu–Zn matrix consists of nano-sized a-brass grains,and the main composition is Cu_3Zn electride.The nano-sized Cu was coated on the surface of tungsten particles by electroless copper plating method,and the fairly low consolidation temperature and short solid-state sintering time result in the nano-sized matrix phase.The dynamic compressive strength of the W–Cu–Zn alloy achieves to1000 MPa,but the alloy shows poor ductility due to the formation of the hard and brittle Cu_3Zn electrides.The fine-grain strengthening and the solution strengthening of the Cu–Zn matrix phase are responsible for the high Vickers microhardness of about 300 MPa for W–Cu–Zn alloy.     

Friction welding of Al–Mg–Si alloy to Ni–Cr–Mo low alloy steel

Abstract

It is difficult to weld the dissimilar material combination of aluminium alloys and low alloy steels using fusion welding processes, on account of the formation of a brittle interlayer composed of intermetallic compound phases and the significant difference in physical and mechanical properties. In the present work an attempt has been made to join these materials via the friction welding method, i.e. one of the solid phase joining processes. In particular, the present paper describes the optimisation of friction welding parameters so that the intermetallic layer is narrow and joints of acceptable quality can be produced for a dissimilar joint between Al-Mg-Si alloy (AA6061) and Ni-Cr-Mo low alloy steel, using a design of experiment method. The effect of post-weld heat treatment on the tensile strength of the joints was then clarified. It was concluded that the friction time strongly affected the joint tensile strength, the latter decreasing rapidly with increasing friction time. The highest strength was achieved using the shortest friction time. The highest joint strength was greater than that of the AA6061 substrate in the as welded condition. This is due to the narrow width of the brittle intermetallic layer generated, which progressed from the peripheral (outer surface) region to the centreline region of the joint with increasing friction time. The joints in the as welded condition could be bent without cracking in a bend test. The joint tensile strength in the as welded condition was increased by heat treatment at 423 K (150° C), and then it decreased when the heat treatment temperature exceeded 423 K. All joints fractured in the AA6061 substrate adjacent to the interface except for the joints heated at 773 K (500° C). The joints fractured at the interface because of the occurrence of a brittle intermetallic compound phase.     

Microstructure and properties of nanocrystalline Fe–Zr–Nb–B soft magnetic alloys with low magnetostriction

We have investigated the microstructure–property relationship of nanocrystalline Fe₈₅Zr_1.2Nb_5.8B₈ and Fe_85.5Zr₂Nb₄B_8.5 soft magnetic alloys in order to understand the origin of drastic change in the permeability regardless of the zero magnetostriction in these two alloy compositions. Plan-view and cross-section transmission electron microscopy (TEM) observations showed strongly textured α-Fe particles on the free surface of the Fe₈₅Zr_1.2Nb_5.8B₈ alloy ribbon, while uniform nanocrystalline microstructure was observed in the Fe_85.5Zr₂Nb₄B_8.5 alloy ribbon. The high Zr content of the latter improves the glass forming ability, thereby suppressing the surface crystallization, resulting in higher permeability. By adding Cu in the Fe–Zr–Nb–B alloy, uniform nanocrystalline microstructure was obtained, from which superior soft magnetic properties with zero magnetostriction was achieved.     

On process–structure–property interconnection in anti-phase synchronised twin-wire GMAW of low carbon steel

The paper investigates process–structure–property interconnection in anti-phase synchronised twin-wire gas metal arc welded low carbon steel samples wherein process variation is achieved by using similar and dissimilar currents and diameters at lead and trail wires. Scanning electron microscopy and microhardness measurements are used as characterisation techniques. The investigation offers new observations on heat generation and distribution in twin-wire welding that affect weld bead and microstructure formation due to changes in arc phenomenon and molten metal flow in weld pool. Use of dissimilar currents facilitates effective utilisation of heat. The two-stage arcing in twin-wire welding facilitates slow heating and cooling that leads to weld metal and heat affected zone softening. A combination of polygonal ferrite, pearlite and bainite with varying compositions is observed across the weldment. A higher current value and larger wire diameter at the lead wire leads to coarsening of the grains thereby reducing the hardness.     

Microstructure and mechanical properties of Ti–Nb–Fe–Zr alloys with high strength and low elastic modulus

Zr was added to Ti–Nb–Fe alloys to develop low elastic modulus and high strength β-Ti alloys for biomedical applications. Ingots of Ti–12Nb–2Fe–(2, 4, 6, 8, 10)Zr (at.%) were prepared by arc melting and then subjected to homogenization, cold rolling, and solution treatments. The phases and microstructures of the alloys were analyzed by optical microscopy, X-ray diffraction, and transmission electron microscopy. The mechanical properties were measured by tensile tests. The results indicate that Zr and Fe cause a remarkable solid-solution strengthening effect on the alloys; thus, all the alloys show yield and ultimate tensile strengths higher than 510 MPa and 730 MPa, respectively. Zr plays a weak role in the deformation mechanism. Further, twinning occurs in all the deformed alloys and is beneficial to both strength and plasticity. Ti–12Nb–2Fe–(8, 10)Zr alloys with metastable β phases show low elastic modulus, high tensile strength, and good plasticity and are suitable candidate materials for biomedical implants.     

Kinetic process of oxidative leaching of chalcopyrite under low oxygen pressure and low temperature

Kinetic process of oxidative leaching of chalcopyrite in chloride acid hydroxide medium under oxygen pressure and low temperature was investigated. The effect on leaching rate of chalcopyrite caused by these factors such as ore granularity, vitriol concentration, sodium chloride concentration, oxygen pressure and temperature was discussed. The results show that the leaching rate of chalcopyrite increases with decreasing the ore granularity. At the early stage of oxidative reaction, the copper leaching rate increases with increasing the oxygen pressure and dosage of vitriol concentration, while oxygen pressure affects leaching less at the later stage. At low temperature, the earlier oxidative leaching process of chalcopyrite is controlled by chemical reactions while the later one by diffusion. The chalcopyrite oxidative leaching rate has close relation with ion concentration in the leaching solution. The higher ion concentration is propitious for chalcopyrite leaching.     

Comparison of tribological properties of industrial low friction coatings

MX2(M= Mo, W; X=S, Se) and DLC (a-C: H and WC/C) are the two kinds of typical low friction coatings widely used in industry. The friction and wear properties of these two kinds of coatings marked as MOVIC,MOST, MoSez/Ni, WSez, a-C: H and WC/C coatings were determined by fretting tests in ambient air of different humidity. The results show that the coefficient of friction of MXz coatings increases when the relative humidity of air increases whereas the coefficient of friction DLC coatings decreases with the increasing of relative humidity. MOVIC and WSe2 coatings have a poor friction and wear resistance because of non-basal planes (100) and ( 101 ) parallel to the surface in the MOVIC coating, or the rough and porous surface of WSe2 coatings. Among these six coatings, MoSe2/Ni and WC/C eoatinas have the highest wear resistance which seems to be unaffected by the relative humidity.     

Plasma-nitriding of tantalum at relatively low temperature

The combined quadratic orthogonal regression method of experiment design was employed to explore the effectsof process parameters of plasma nitriding of tantalum such as total pressure, temperature and original hydrogen molar frac-tion on the hardness, roughness and structure of nitriding surfaces. The regression equations of hardness, roughness andstructure were given according to the results of regression and statistic analysis. And the diffusion activation energy of ni-trogen in tantalum on plasma nitriding conditions was calculated according to the experimental data of hardness ofplasma-nitriding of tantalum vs time and temperature. The diffusion activation energy calculated belongs to (155.49±10.51)kJ/mol(783-983K).     

Evaluation of the deviation angle of ferrite from the Kudjumov–Sachs relationship in a low carbon steel by EBSD

A method to evaluate the orientational relationships between ferrite and the mother austenite grain is proposed. The deviation angles from the Kudjumov–Sachs relationships were evaluated based on the orientation of the austenite grains, which is indirectly determined from the orientations of martensite packets formed within the austenite grains.     

High-power (Nd,Dy)–(Fe,Co)–B magnets with a low temperature coefficient of induction

High-power (Nd, Dy)–(Fe, Co)–B permanent magnets with a low temperature coefficient of induction (α) were prepared using advantages of strip casting and low-oxygen technologies. The microstructure and temperature dependences of magnetic properties have been studied on sintered (Nd_{1 – x} Dy _x )_13.9(Fe_{1 – y} Co _y )_79.8Cu_0.1Ga_0.1B_6.1 magnets with 0.20 ≤ x ≤ 0.25 and 0 ≤ y ≤ 0.20. The increase in y from 0 to 0.20 is accompanied by an increase in the Curie temperature from 327 to 492°C. This favors a decrease in the value of α from 0.099 to 0.060%/°C, respectively. Magnets with an oxygen content of no more than 2500 ppm which were prepared from the (Nd_0.75Dy_0.25)_13.9(Fe_0.85Co_0.15)_79.8Cu_0.1 Ga_0.1B_6.1 alloy, have the following hysteresis characteristics at 140°C: B _r ≥ 11.3 kG, H _c ≥ 8 kOe, and (BH)_max ≥ 30 MGOe; in this case, α ≤ |–0.07%/°С|.     

Microstructure and storage properties of low V-containing Ti–Cr–V hydrogen storage alloys prepared by arc melting and suction casting

The microstructure and hydrogen storage properties of low V content （Ti0.46Cr0.54）100-xVx （x = 2.5-7.1, at%） and （TiyCr1-y）95V5 （y= 0.38-0.54） alloys were investigated. These alloys were prepared by arc melting and copper mould suction casting. The structures of as-cast （Ti0.46Cr0.54）100-xVx （x = 2.5, 5.0, and 7.1） alloy ingots evolve with V contents from pure Laves-（x = 2.5） to dual-phase TiCr2-BCC structures （5.0 and 7.1）, whereas the suction-cast （Ti0.46Cr0.54）100-xVx （x =2.5, 5.0, and 7.1） alloys only contain single BCC phase. The suction-cast alloy rod （Ti0.46Cr0.54）95V5, containing only 5.0 at% V is shown to possess the optimum hydrogen absorption capacity, with the maximum hydrogen content of 3.14 wt%. Furthermore, the hydrogen storage properties of the suction-cast low V alloys （TiyCr1-y）95V5 （y = 0.38-0.54） are sensitive to Ti/Cr ratios and only those alloys with Ti/Cr ratios close to the CN14 cluster [TiTCrs] have good hydrogen storage properties.     

Preparation of aluminide coatings at relatively low temperatures

1 Introduction Protective coatings by pack aluminizing are frequently applied to metals to protect them from high temperature oxidation and hot corrosion attack [1, 2]. Pack aluminizing consists of heating the parts to be coated in a closed or vented pac…     

Nanoscale smooth interface maintained metallisation of polyimide using low concentration ozone micro–nano bubbles dispersed in water

In order to induce adhesion of electroless CuNiP deposition to polyimide (PI) film substrate, surface modification of PI film with an aqueous dispersion of ozone micro–nano bubbles was investigated. The treatment resulted in maximum adhesion strength of 1·14 kN m^?1 for a treatment time of 5 min. Structure of the modified PI surface, the PI/plating interface, mechanism for adhesion and laminate properties were analysed. Despite increased adhesion, surface roughness of PI was not notably changed by the ozone induced surface modification. Contact of PI surface with high ozone concentration micro–nano bubbles with sufficient frequency was found to modify the surface with a low total ozone concentration of the aqueous dispersion. Cross-sectional observation of the interface suggested that formation of a thin nanoporous anchor layer on the PI surface was responsible for plating adhesion. This method provides an environment friendly and improved process for plating on PI using low concentration ozone treatment.     

Characterization of oxide structures formed on nickel-chromium alloy during low pressure oxidation at 500–600°C

Low pressure oxidation studies of Ni-18%Cr alloy were carried out at temperatures of 500–600°C for very brief periods. Detailed XPS, AES, SEM, and TEM studies identified four stages in the initial oxidation. These are: (1) formation of a mixed nickel-chromium oxide overlayer; (2) growth of submicron-sized oxide nodules; (3) development of dark hole-like patches on the surface; and (4) growth of second generation oxide nodules. Both types of nodules consist primarily of a nickel structure depleted in oxygen. Their formation appears to result from a very rapid outward movement of nickel from localized defects in the metal. The dark patches result from the presence of a chromium oxide-rich underlayer, which appears to form by a lateral migration of chromium from adjacent oxide/metal interface regions and from grain boundaries.     

Microstructure of martensite–austenite constituents in heat affected zones of high strength low alloy steel welds in relation to toughness properties

Abstract

Microstructure and fracture properties relationships have been investigated in the heat affected zones (HAZs) of a high strength low alloy steel used for offshore applications. Metallographic examinations of simulated HAZ microstructures were conducted to investigate the detailed microstructure of the martensite–austenite (M–A) constituents. Using scanning and transmission electron microscopy, various microstructures were found for the M–A constituents. In mixed particles, retained austenite was located at the periphery of the islands. Chemical and/or mechanical effects could possibly account for the stabilisation of this austenite phase. In situ cooling experiments in the transmission electron microscope showed that stacking faults play an important role in the thermal stability of austenite. Impact properties of simulated HAZ microstructures are strongly affected by both the bainitic microstructure and M–A constituents. In particular, freshly transformed high carbon martensite was shown to be much more deleterious than retained austenite.     

Effects of heat treatment on properties of multi-element low alloy wear-resistant steel

The paper has studied the mechanical properties and heat treatment effects on multi-element low alloy wear-resistant steel (MLAWS) used as a material for the liner of rolling mill torii. The results show that when quenched at 900-920℃ and tempered at 350-370℃, the MLAWS has achieved hardness above 60 HRC, tensile strength greater than 1 600 MPa, impact toughness higher than 18J/cm2 and fracture toughness greater than 37 MPa·m1/2. When the quenching temperature is lower than 900℃, the hardness of the MLAWS increases with the temperature. When the quenching temperature is higher than 900℃, the hardness decreases with the increase of temperature. At a quenching temperature below 920℃, the effect of quenching temperature on the impact toughness is not obvious. In quenching at above 920℃, impact toughness decreases as the temperature increases. When the tempering temperature is exceeding 450℃, the hardness begins to decrease significantly. Tempering at 350℃ has produced the best wear resistance on the MLAWS.     

Synthesis of photocatalytic TiO2 nanoparticles at low cost

Anatase TiO2 nanoparticles were synthesized by using HTiO3 as raw material and adopting TiOSO4 solution neutralizing process. The results show that the hydrolytic reaction temperature and time, molar ratio of urea to Ti precursors （R）, volume ratio of distilled water to the TiOSO4 solution （F） determine the yield of TiO2; the average crystalline size of TiO2 nanoparticles can be controlled through the sintering temperature and the optimum temperature is about 600 ℃; the TiO2 particles have good photocatalytic activity for decolorization of methyl orange.     

In-situ formation of Al-CaB_6 composites with low resistivity

In this work, in-situ CaB6 reinforced aluminum matrix composites were fabricated, and the microstructure, resistivity, microhardness and coefficient of thermal expansion (CTE) of Al-CaB6 composites were studied. It is found that CaB6 compounds can be formed by reducing reaction occurred in the Al melt: . CaB6 exhibits a hexahedron morphology and distributes uniformly in the Al alloy matrix. The resistivity of Al-CaB6 composites is 3.02*10-8 Ω·m, which is close to that of pure Al and lower than that of 6063A...     

The effect of potential on the high-temperature fatigue crack growth response of low alloy steels,part 2: sulfide–potential interaction

Environmentally assisted cracking (EAC) of low-alloy steels exposed to high temperature dehydrogenated water was found to be dependent on externally applied potential. EAC became active when the specimen was polarized anodically above a critical potential, which was not a function of steels sulfur. However, the plateau crack propagation rate was determined to be dependent on both overpotential and steels sulfur concentration. Hydrogen additions inhibited the ability of applied potential to activate EAC. The behavior was related to the formation of hydrogen ions on the specimen surface through hydrogen oxidation during anodic polarization. A mechanism based on the formation of hydrogen sulfide at the crack tip and hydrogen ions at the crack mouth is presented to describe the process by which sulfides and hydrogen ions affect the critical sulfide concentration at the crack tip needed to establish EAC.