Elements inter-diffusion in the turning of wear-resistance aluminum bronze

Inter-diffusion of elements between the tool and the workpiece during the turning of aluminum bronze using high-speed steel and cemented carbide tools have been studied. The tool wear samples were prepared by using M2 high-speed steel and YW1 cemented carbide tools to turn a novel high strength, wear-resistance aluminum bronze without coolant and lubricant. Adhesion of workpiece materials was found on all tools' surface. The diffusion couples made of tool materials and aluminum bronze were prepared to simulate the inter-diffusion during the machining. The results obtained from tool wear samples were compared with those obtained from diffusion couples. Strong inter-diffusion between the tool materials and the aluminum bronze was observed in all samples. It is concluded that diffusion plays a significant role in the tool wear mechanism.     

Diffusion welding of SiCp/2014Al composites using Ni as interlayer

SiCp/2014Al composites were bonded with the vacuum diffusion welding technique using Ni as the interlayer metal. Ni and Al were interdiffused and there were intermetallic compounds formed in the inter transition layer, which was composed of Ni₃Al//NiAl//NiAl₃. The relation between the diffusion distance and the element concentration was calculated according to Fick’s second law. The relations of the diffusion concentration and the diffusion welding technique parameters were calculated.     

Solid state interfacial reactions in electrodeposited Ni/Sn couples

Ni/Sn couples, prepared by sequentially electroplating Ni layers and Sn layers on metallized Si wafers, were employed to study the microstructures and growth kinetics of Ni-Sn intermediate phases, when the Ni/Sn couples were aged at room temperature or annealed at temperatures from 150 to 225℃ for various times. The results show that the NiSn phase and Ni₃Sn₄ phase are formed, respectively, in the aged couples and annealed couples. The Ni₃Sn₄ layer is continuously distributed between the Ni and Sn sides in the annealed Ni/Sn couples. The Ni₃Sn₄ growth follows parabolic growth kinetics with an apparent activation energy of 39.0 kJ/mol.     

Solidification structures of high niobium containing TiAl alloys

To understand the effect of alloy stoichiometry on the microstructural development and mechanical behavior of γ-TiAl-based materials, it is necessary to have a determination of the phase relationships for the TiAl alloy system near the γ phase field. Cast structures and phases of Ti-(43-47)Al-8Nb-(1-2)Mn (at%) alloys have been studied by using scanning electron microscope and X-ray diffraction. Their solidification path and microstructure development during the solidification were analyzed. The experimental results show that the alloys with different Al contents form different macrostructures and microstructural morphologies. This indi-cates that the solidification paths are different with different Al contents. The alloy with 43Al forms equiaxed grain structure, and the solidification path is as follows:L→L+β→β→α+β→α+β cores→α₂+γ+B2 cores. Whereas the alloy with 47Al forms colum-nar grain structure, and the solidification path is as follows:L→L+β→α+β+L→α+γ+β cores→tXj+γ+BZ cores. The p phase is their primary solid phase and can be retained to ambient temperature. The alloy with 43Al solidifies completely into β phase. The peritectic reactions L+P→α and L+α→γ appear when the Al content increases to 47Al.     

Influence of FeO and sulfur on solid state reaction between MnO-SiO2-FeO oxides and an Fe-Mn-Si solid alloy during heat treatment at 1473 K

To clarify the influence of FeO and sulfur on solid state reaction between an Fe?Mn?Si alloy and MnO?SiO2?FeO oxides under the restricted oxygen diffusion flux, two diffusion couples with different sulfur contents in the oxides were produced and investigated after heat treatment at 1473 K. The experimental results were also compared with previous work in which the oxides contained higher FeO. It was found that although the FeO content in the oxides decreased from 3wt% to 1wt% which was lower than the content corresponding to the equilibrium with molten steel at 1873 K, excess oxygen still diffused from the oxides to solid steel during heat treatment at 1473 K and formed oxide particles. In addition, increasing the sulfur content in the oxides was observed to suppress the diffusion of oxygen between the alloy and the oxides.     

Galvanic corrosion behavior of die cast AZ91D magnesium alloy in chloride solution

The galvanic corrosion behavior of die cast AZ91D magnesium alloy coupled with H62 brass, 316L stainless steel, A3 steel and LY12 aluminum alloy of different areas in 3.5% NaCl solution was studied. The free corrosion potentials, galvanic potentials and currents of these galvanic couples were measured. The galvanic effects were determined by the mass loss and regression method using three points. The results show that: (1) In these four kinds of couples AZ91D acts as the anode, whose galvanic corrosion behavior is mainly controlled by the cathodic polarization; (2) The free corrosion potentials of these four kinds of couples change a liffle with time and cathodic/anodic area ratio (CAAR); (3) The galvanic potential of AZ91D/LY12 moves positively with the increase of time and CAAR; (4) The galvanic currents increase with CAAR, but there is difference in the current change between different couples; (5) The anodic dissolution rate of the magnesium alloy increases by 2-3 orders after being coupled with these four kinds of metals and the galvanic effects of these couples have such a relation as γ_H62>γ_316LS.S>γ_LY12>γ_A3.     

In situ (α-Al2O3+ZrB2)/Al composites with network distribution fabricated by reaction hot pressing

In situ (α-Al2O3+ZrB2)/Al composites with network distribution were fabricated using low-energy ball milling and reaction hot pressing. Differential thermal analysis (DTA) was used to study the reaction mechanisms in the Al–ZrO2–B system. X-ray diffraction (XRD) and scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDX) were used to investigate the composite phases, morphology, and microstructure of the composites. The effect of matrix network size on the microstructure and mechani-cal properties was investigated.The results show that the optimum sintering parameters to complete reactions in the Al–ZrO2–B system are 850℃ and 60 min.In situ-synthesizedα-Al2O3 and ZrB2 particles are dispersed uniformly around Al particles, forming a network micro-structure; the diameters of theα-Al2O3 and ZrB2 particles are approximately 1–3μm. When the size of Al powder increases from 60–110μm to 150–300μm, the overall surface contact between Al powders and reactants decreases, thereby increasing the local volume fraction of re-inforcements from 12% to 21%. This increase of the local volume leads to a significant increase in microhardness of thein situ (α-Al2O3–ZrB2)/Al composites from Hv 163 to Hv 251.     

Investigation on the interface of Cu/Al couples during isothermal heating

The evolutionary process and intermetallic compounds of Cu/Al couples during isothermal heating at a constant bonding temperature of 550℃ were investigated in this paper. The interfacial morphologies and microstructures were examined by optical microscopy, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, and X-ray diffraction. The results suggest that bonding is not achieved between Cu and Al at 550℃ in 10 min due to undamaged oxide films. Upon increasing the bonding time from 15 to 25 min, however, metallurgical bonding is obtained in these samples, and the thickness of the reactive zone varies with holding time. In the interfacial region, the final microstructure consists of Cu₉Al₄, CuAl, CuAl₂, and α-Al + CuAl₂. Furthermore, these results provide new insights into the mechanism of the interfacial reaction between Cu and Al. Microhardness measurements show that the chemical composition exerts a significant influence on the mechanical properties of Cu/Al couples.     

Near-infrared to visible up-conversion emissions of Er^3＋ doped Al2O3 powders derived from the sol-gel method

The Er3 doped Al2O3 powders were prepared by the sol-gel method using the aluminium isopropoxide [Al(OC3H7)3]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)3.5H2O]. The different phase structure, including three crystalline types of (Al,Er)2O3 phases, γ, θ, α, and two Er-Al-O phases, ErAlO3 and Al10Er6O24, was obtained with the 1 mol% Er3 doped Al2O3 powders at the different sintering temperatures of 600―1200℃. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the 2H11/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3 , were detected by a 978 nm semiconductor laser diodes excitation. The phase structure and OH content had evident influence on the up-conversion emissions intensity. The maximum intensities of both the green and red emissions were obtained respectively for the Er3 doped Al2O3 powders sintered at 1200 ℃, which was composed mainly of α-(Al,Er)2O3, less of ErAlO3 and Al10Er6O24 phases, and with the least OH content. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er3 doped Al2O3 powders.     

Microstructure and mechanical properties of twin-wire arc sprayed Ni-Al composite coatings on 6061-T6 aluminum alloy sheet

We have systematically studied the microstructure and mechanical properties of Ni-5wt%Al and Ni-20wt%Al composite coatings fabricated on 6061-T6 aluminum alloy sheet by twin-wire arc spraying under different experimental conditions. The abrasive wear behavior and interface diffusion behavior of the composite coatings were evaluated by dry/wet rubber wheel abrasive wear tests and heat treatment, respectively. Experimental results indicate that the composite coatings exhibit features of adhesive wear. Besides, the Vickers microhardness of NiAl and Ni₃Al intermetallic compounds is relatively larger than that of the substrate, which is beneficial for enhancing the wear resistance. With the increase of annealing temperature and time, the interface diffusion area between the Ni-Al coating and the substrate gradually expands with the formation of NiAl₃ and Ni₂Al₃ phases, and is controlled by diffusion of aluminum atoms. The grain growth exponent n of diffusion kinetics of the Ni-Al coating, calculated via a high-temperature diffusion model at 400, 480, and 550℃, is between 0.28 and 0.38. This satisfies the cubic law, which is consistent with the general theoretical relationship of high-temperature diffusion.     

In situ(α-Al_2O_3+ZrB_2)/Al composites with network distribution fabricated by reaction hot pressing

In situ(α-Al_2O_3+ZrB_2)/Al composites with network distribution were fabricated using low-energy ball milling and reaction hot pressing. Differential thermal analysis(DTA) was used to study the reaction mechanisms in the Al–Zr O2–B system. X-ray diffraction(XRD) and scanning electron microscopy(SEM) in conjunction with energy-dispersive X-ray spectroscopy(EDX) were used to investigate the composite phases, morphology, and microstructure of the composites. The effect of matrix network size on the microstructure and mechanical properties was investigated. The results show that the optimum sintering parameters to complete reactions in the Al–Zr O2–B system are 850°C and 60 min. In situ-synthesized α-Al2O3 and Zr B2 particles are dispersed uniformly around Al particles, forming a network microstructure; the diameters of the α-Al2O3 and Zr B2 particles are approximately 1–3 μm. When the size of Al powder increases from 60–110 μm to 150–300 μm, the overall surface contact between Al powders and reactants decreases, thereby increasing the local volume fraction of reinforcements from 12% to 21%. This increase of the local volume leads to a significant increase in microhardness of the in situ(α-Al2O3–Zr B2)/Al composites from Hv 163 to Hv 251.     

Preliminary study on interaction of water mist with diffusion flame of liquid fuels

The chemical and physical interaction mechanisms of the water mist with diffusion flame of liquid fuels are investigated.The difference of the thermograms and the thermal field isograms between ethanol flame and kerosene flame with the water mist applica-tion is explained. With the water mist application, the differences between ethanol and kerosene in heat release rate, O_2 and CO concentra-tions of their combustion products, and the temperature of their srnoke are analyzed. At the same time, the interaction mechanism of thewater mist with diffusion flame is presented and their relationship to the fuel species and to the concentration of water mist is described.     

Phase field simulation of interatomic potentials for double phase competition during early stage precipitation

Phase field model was employed to study the variations of interatomic potentials of Ni 3 Al (L1 2 phase) and Ni 3 V (DO 22 phase) as a function of temperature and concentration. The long-range order (LRO) parameter related interatomic potentials equations formulated by Khachaturyan were utilized to establish the inversion equations for L1 2 and DO 22 phases, with which interatomic potentials could be calculated. The interatomic potentials of Ni-Al and Ni-V exhibited approximately linear increases and decreases, individually, with enhanced Al concentration. Substituting the inverted interatomic potentials into the microscopic phase field equations led to three cases of precipitation sequence: the DO 22 phase preceded L1 2 phase precipitating at the interatomic potentials of Ni-V > Ni-Al; the vice cases; and two phases precipitated simultaneously at interatomic potentials of Ni-V and Ni-Al were equal.     

Growth characteristics of directionally solidified Al2O3/YAG/ZrO2 ternary hypereutectic in situ composites under ultra-high temperature gradient

Oxide eutectic ceramic in situ composites have attracted significant interest in the application of high-temperature structural materials because of their excellent high-temperature strength,oxidation and creep resistance,as well as outstanding microstructural stability.The directionally solidified ternary Al2O3/YAG/ZrO2 hypereutectic in situ composite was successfully prepared by a laser zone remelting method,aiming to investigate the growth characteristic under ultra-high temperature gradient.The microstructures and phase composition of the as-solidified hypereutectic were characterized by using scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD).The results show that the composite presents a typical hypereutectic lamellar microstructure consisting of fine Al2O3 and YAG phases,and the enriched ZrO2 phases with smaller sizes are randomly distributed at the Al2O3/YAG interface and in Al2O3 phases.Laser power and scanning rate strongly affect the sample quality and microstructure characteristic.Additionally,coarse colony microstructures were also observed,and their formation and the effect of temperature gradient on the microstructure were discussed.     

Synthesis and performance of Ca-α/β-SiAlON composites from tailings

Ca-α/β-SiAlON composites were prepared using Ca-α/β-SiAlON powder synthesized from gold ore tailings, which contained abundant Si and Al elements as the major raw materials together with minor additives, through a pressure-less sintering method. The influences of sintering temperature on the phase composition and microstructure of the composites were analyzed. The scanning electron microscopy images of the composites show the interlacing of grains with elongated columnar, short columnar and plate-like morphologies. The composites sintered at 1520℃ for 6 h have a flexural strength of 352 MPa, Vickers hardness of 11.2 GPa, and fracture toughness of 4.8 MPa·m1/2. The relative content of each phase in the products is I(Ca-α-SiAlON):I(β-SiAlON):I(Fe₃Si) = 23:74:3, where I_i stands for the diffraction peak intensity of phase i.     

Influence of substrate metals on the crystal growth of AlN films

AlN films were deposited by reactive radio frequency (RF) sputtering on various bottom electrodes, such as Al, Ti, Mo, Au/Ti, and Pt/Ti. The effects of substrate metals on the orientation of AlN thin films were investigated. The results of X-ray diffraction, atomic force microscopy, and field emission scanning electron microscopy show that the orientation of AlN films depends on the kinds of substrate metals evidently. The differences of AlN films deposited on various metal electrodes are attributed to the differences in lattice mismatch and thermal expansion coefficient between the AlN material and substrate metals. The AlN film deposited on the Pt/Ti electrode reveals highly the c-axis orientation with well-textured columnar structure. The positive role of the Pt/Ti electrode in achieving the high-quality AlN films and high-performance film bulk acoustic resonator (FBAR) may be attributed to the smaller lattice mismatch as well as the similarity of thermal expansion coefficient between the deposited AlN material and the Pt/Ti electrode substrate.     

Microstructures and mechanical properties of as-extruded Mg–5Sn–1Zn–xAl(x=1, 3 and 5) alloys

As-extruded Mg–5Sn–1Zn–xAl alloys(x=1, 3, and 5) were fabricated by hot extrusion. The experimental results revealed that the yield strength of alloys initially decreased and then increased with the increase of Al content. These changes were mainly attributed to the difference in crystallographic texture and volume fractions of second phases. The ultimate tensile strength, yield strength, and elongation of the alloys were greater than 310 MPa, 227 MPa, and 11%, respectively. The strain hardening ability of the alloys was also discussed.     

Microstructures and mechanical properties of a new titanium alloy for surgical implant application

A new titanium alloy Ti12.5Zr2.5Nb2.5Ta (TZNT) for surgical implant application was synthesized and fully annealed at 700℃ for 45 min. The microstructure and the mechanical properties such as tensile properties and fatigue properties were investigated. The results show that TZNT mainly consists of a lot of lamella α-phase clusters with different orientations distributed in the original β-phase grain boundaries and a small amount of β phases between the lamella α phases. The alloy exhibits better ductility, lower modulus of elasticity, and lower admission strain in comparison with Ti6Al4V and Ti6Al7Nb, indicating that it has better biomechanical compatibility with human bones. The fatigue limit of TZNT is 333 MPa, at which the specimen has not failed at 107 cycles. A large number of striations present in the stable fatigue crack propagation area, and many dimples in the fast fatigue crack propagation area are observed, indicating the ductile fracture of the new alloy.     

Coarsening behavior of γ′ and γ″ phases in GH4169 superalloy by electric field treatment

The coarsening behaviors of γ′ and γ″ phases in GH4169 alloy aged at 1023 and 1073 K with electric field treatment (EFT) were investigated by transmission electron microscopy (TEM) and positron annihilation lifetime spectroscopy (PALS). It is demonstrated that precipitation coarsening occurs, and the growth activation energies of γ′ and γ″ phases can be decreased to 115.6 and 198.1 kJ·mol?1, respectively, by applying the electric field. The formation of a large number of vacancies in the matrix is induced by EFT. Due to the occurrence of vacancy migration, the diffusion coefficients of Al and Nb atoms are increased to be 1.6–5.0 times larger than those without EFT at 1023 or 1073 K. Furthermore, the formation of vacancy clusters is promoted by EFT, and the increase in strain energy for the coarsening of γ′ and γ″ phases can be counterbalanced by the formation of vacancy clusters.     

铝基复合材料界面Al?Ce?Cu?W非晶层的热驱动固相非晶化研究

Interfacial Al?Ce?Cu?W amorphous layers formed through thermally driven solid-state amorphization within the (W+CeO₂)/2024Al composite were investigated. The elemental distributions and interfacial microstructures were examined with an electron probe microanalyzer and a high-resolution transmission electron microscope, respectively. The consolidation of composites consisted of two thermal processes: vacuum degassing (VD) and hot isostatic pressing (HIP). During consolidation, not only the three major elements (Al, W, and Ce) but also the alloying elements (Mg and Cu) in the Al matrix contributed to amorphization. At VD and HIP temperatures of 723 K and 763 K, interfacial amorphous layers were formed within the composite. Three diffusion processes were necessary for interfacial amorphization: (a) long-range diffusion of Mg from the Al matrix to the interfaces during VD; (b) long-range diffusion of Cu from the Al matrix to the interfaces during HIP; (c) short-range diffusion of W toward the Al matrix during HIP. The newly formed interfacial Al?Ce?Cu?W amorphous layers can be categorized under the Al?Ce?TM (TM: transition metals) amorphous system.