Microstructure and mechanical properties of tungsten inert gas welded–brazed Al/Ti joints

The tungsten inert gas welding–brazing process using Al-based filler metal has been developed for joining 5052 Al alloy to Ti–6Al–4V alloy in a butt configuration. The results indicated that heat input influenced the morphology and thickness of the interfacial reaction layer of Al/Ti joints, which played an important role in the mechanical properties of weldment. With the optimised tungsten electrode offset D of 1.0?mm from Al/Ti initial interface to Al side and welding current of 70?A, the thin cellular-shaped and club-shaped TiAl₃ reaction layers formed in the brazing zone, which contributed to suppressing crack initiation and propagation during tensile test. Eventually, the maximum tensile strength of 183?MPa was obtained and the optimised Al/Ti joint fractured at Al alloy base plate. Moreover, the power density characterisation and joining mechanism of Al/Ti joints were discussed.     

Microstructure evolution and mechanical properties of Cu–Al joints by ultrasonic welding

Dissimilar joints of copper to aluminium were produced by high power ultrasonic welding (USW). The interfacial reaction between copper and 6061 aluminium alloy as a function of welding time was studied. The intermetallic compound (IMC) layer is mainly composed of CuAl₂ and Cu₉Al₄. The thickness of the IMC layer increases with the welding time. For a relatively long welding time (0·7 s) in USW, the dendritic solidification microstructure was observed in local regions, owing to the occurrence of the eutectic reaction, α-Al+θ→L, in the welding process. The lap shear load (or strength) of the joints first increases and then decreases with increasing welding time, and the failure of the joints occurred dominantly at the interface. This is mainly attributed to the development of IMC layer at the interface.     

Microstructure and properties of WC–Co/3Cr13 joints brazed using Ni electroplated interlayer

The brazed joints of WC–Co cemented carbide and 3Cr13 stainless steel using Ni electroplated on Cu–Zn alloy as interlayer were investigated. The shear strength of the WC–Co/interlayer/3Cr13 joints increased firstly and then decreased with the increase of brazing temperature or brazing time. The maximum shear strength value of the brazed joints was 154 MPa at 1100 °C for 10 min. The characterizations of the WC–Co/interlayer/3Cr13 joints were studied by SEM, EDS and XRD. The results showed that the brazed joints fractured in the bulk WC–Co substrates near the interlayer. The added Ni promoted the formation of interdiffusion zone, which possessed positive effects on the bond strength of the WC–Co/interlayer/3Cr13 joints. Austenite solid solution was formed in the WC–Co/interlayer/3Cr13 joint, and the majority of austenite solid solution presented as columnar crystal. The number of austenite crystals on the WC–Co/interlayer interface was tremendously more than that on the interlayer/3Cr13 interface.     

Microstructure and mechanical properties of friction stir processed Al−Mg2Si alloys

The microstructure and mechanical properties of friction stir processed Al−Mg₂Si alloys were studied by TEM and EBSD. The results showed that an increase in the tool rotation speed (300−700 r/min) led to a decrease in the defect area (from 10.5 mm² to zero), whereas the defect area demonstrated the opposite trend (increased to 1.5 mm² from zero) upon further increasing the rotation speed (700−1200 r/min). The types of defects were transformed from tunnel defects to fusion defects as the rotational speed increased. The coarse Mg₂Si dendrites were broken and fine particles (smaller than 10 μm) formed in the weld nugget (WN). The amount of low-angle grain boundaries increased significantly from 57.7% to 83.6%, which was caused by an increase in the content of the deformed structure (from 1.7% to 13.6%). The hardness, ultimate tensile strength (UTS) and elongation were all greatly improved for the weld nugget. The hardness values of the WNs had the following order: R300<R1200<R500<R900<R700. The UTS and elongation had the following order: BM (base material)<R300<R1200<R500<R900<R700. The UTS and the elongation for the WN were increased by one and three times, respectively.     

Microstructure and mechanical properties of tungsten inert gas welded–brazed Mg/Ti lap joints

The tungsten inert gas (TIG) welding–brazing technology using Mg based filler was developed to join AZ31B Mg alloy to TA2 pure Ti in a lap configuration. The results indicate that robust joints can be obtained with welding current in the range of 60–70 A and welding speed of 0·2 m min^?1. The joints were found to be composed of the coarse grained fusion zone accompanied with the precipitated phase of Mg₁₇Al₁₂, and a distributed Mg–Ti solid solution zone at the interface of Mg/Ti, indicating that metallurgical bonding was achieved. The maximum tensile–shear strength of 193·5 N mm^?1, representing 82·3% joint efficiency relative to the Mg alloy base metal, was attained. The optimised Mg/Ti joint fractured at Mg fusion zone upon tensile–shear loading, mainly caused by grain coarsening. Moreover, the fracture surface practically consisted of scraggly areas, which was characterised by equiaxed dimple patterns accompanied with a few lamellar tearing.     

Microstructure and mechanical properties of Ni3Al and Ni3Al–1B alloys fabricated by SHS/HE

The well-densified Ni₃Al alloys without and with boron addition were fabricated by self-propagation high-temperature synthesis and hot extrusion (SHS/HE) technology. Microstructure investigation showed that Ni₃Al and Ni₃Al-1B alloys contained fine grain structure. Analysis of X-ray spectra as well as transmission electron microscopy studies revealed that three phases present in all alloys: γ-Ni, Ni₃Al and dispersoids of α- Al₂O₃ and γ- Al₂O₃. However, β-NiAl, Ni₃B phase and twinned Ni₃Al crystal are observed in the Ni₃Al-1B alloy. In addition, dislocations with high density exist in all alloys. The mechanical test showed that the B addition leads to obvious improvement in yield strength and compressive ductility, and compared with the ones synthesized by combustion, SHS/HE synthesized Ni₃Al and Ni₃Al-1B alloys exhibit more excellent mechanical properties.     

Microstructure and mechanical properties of Fe–Si–Ti–(Cu,Al) heterostructured ultrafine composites

The influence of partial substitution of Fe by Cu or Al in Fe_75?xSi₁₅Ti₁₀(Cu, Al)_x (x = 0 and 4) ultrafine composites on the microstructure and mechanical properties has been investigated. The Fe₇₁Si₁₅Ti₁₀Cu₄ ultrafine composite exhibits a favorable microstructural evolution and improved mechanical properties, i.e., large plastic strain of ～5% and pronounced work hardening characteristics. The mechanical properties of the ultrafine eutectic composite are strongly linked to the length scale heterogeneity and the distribution of the constituent phases.     

Microstructure and mechanical properties of laser melting deposited Ti2Ni3Si/NiTi Laves alloys

Two Ti2Ni3Si/NiTi Laves phase alloys with chemical compositions ofNi-39Ti-11Si and Ni-42Ti-8Si （%, mole fraction, the same below）, respectively, were fabricated by the laser melting deposition manufacturing process, aiming at studying the effect of Ti, Si contents on microstructure and mechanical properties of the alloys. The Ni-39Ti-llSi alloy consisting of Ti2Ni3Si primary dendrites and Ti2Ni3Si/NiTi eutectic matrix is a conventional hypereutectic Laves phase alloy while the Ni-42Ti-8Si alloy being made up of NiTi primary dendrites uniformly distributed in Ti2Ni3Si/NiTi eutectic is a new hypoeutectic alloy. Mechanical properties of the alloys were investigated by nano-indentation test. The results show that the decrease of Si and the increase of Ti contents change the microstructures of the alloys from hypereutectic to hypoeutectic, which influences the mechanical properties of the alloys remarkably. Corrosion behaviors of the alloys were also evaluated by potentiodynamic anodic polarization curves.     

Microstructure and mechanical performance of brazed joints of Cf/SiC composite and Ti alloy using Ag–Cu–Ti–W

Abstract

C_f/SiC composite was brazed to Ti alloy using interlayer of Ag–Cu–Ti–W mixed powder. The effects of W content and brazing parameters on the microstructure and properties of the brazed joints were investigated. The results show that W grains mainly distribute in Ag phase in the brazing layer and provide the effects of reinforcement and lowering residual thermal stress on the joint. The room temperature and 500°C shear strengths of the joints performed at 500°C for 30 min with Ag–Cu–Ti–50W (vol.-%) are remarkably higher than the optimal strengths of the joints brazed with Ag–Cu–Ti.     

Microstructure of Si3N4/Si3N4 joint brazed using Cu-Pd-Ti alloy filler

Microstructure of the Si3 N4/Si3 N4 joint brazed using an active filler of Cu-Pd-Ti alloy was analyzed by means of EPMA and XRD. The results indicate that a perfect Si3 N4/Si3 N4 joint is obtained by using an active filler of Cu76.5Pd8.5Ti15 alloy with brazing temperature, pressure and holding time of 1 373 - 1 473 K, 2× 10-3 MPa and 1.8 ks, respectively. The filler alloy in the joint is a Cu-Pd solution containing reactant of TiN, PdTiSi and Pd2Si.The interface between the filler alloy and Si3 N4 ceramic is composed of TiN reactant.     

Solidification structure and mechanical properties of Al–Li–Cu–Zr cast alloys

Abstract

The microstructure and properties of three Al–3Li–1Cu ternary alloys have been studied, in particular the effect of Zr additions on the microstructure, precipitation and mechanical properties. The results showed that, for these Al–Li casting alloys, Zr content up to 0.2 wt-% was acceptable, and the Zr additions appeared to refine the grain structure. During aging, the Zr rich phase provided nucleation sites for δ' phase and promoted δ' phase refinement and homogenisation. Under optimised conditions, the tensile strength and elongation to failure of the Al–Li–Cu–Zr casting alloys were 400 MPa and 2.5%, respectively.     

Properties and fracture processes of Si3N4/ Si3N4 joints brazed using Cu–Zn–Ti filler alloy

Abstract

Si₃N₄ ceramic was jointed to itself using a filler alloy of Cu-Zn-Ti at 1123-1323 K for 0.3-2.7 ks. Ti content in the Cu-Zn-Ti filler alloy was varied from 5 to 20 at.-%. The effect of brazing parameters, such as brazing temperature, holding time and Ti content, on the mechanical properties and facture processes of the Si₃N₄/Si₃N₄ joint were investigated. The results indicated that the increased brazing temperature, holding time and Ti content increase the thickness of the interfacial reaction zone in the Si₃N₄/filler alloy, and the size and amount of the reaction phases in the filler alloy. Their increases lead to increasing shear strength of the joint. The fracture behaviour of the Si₃N₄/Si₃N₄ joint greatly depends on the microstructure of the joint. A suitable thick reaction zone with reaction phases yields the high strength of the Si₃N₄/ Si₃N₄ joint.     

Microstructure and strength of brazed joints of TiB2 cermet to TiAl-based alloys

In this study, TiB2 cermet and TiAl-based alloy are vacuum brazed successfully by using Ag-Cu-Ti filler metal.The microstructural analyses indicate that two reaction products, Ti ( Cu, Al ) 2 and Ag bused solid solution ( Ag ( s. s ) ) , are present in the brazing seam, and the iuterface structure of the brazed joint is TiB2/TiB2 Ag ( s. s ) /Ag ( s. s ) Ti ( Cu,Al)2/Ti( Cu, Al)2/TiAl. The experimental results show that the shear strength of the brazed TiB2/TiAl joints decreases us thebrazing time increases at a definite brazing temperature. When the joint is brazed at 1 223 K for 5 min, a joint strength up to 173 MPa is achieved.     

Microstructure,mechanical properties and two-body abrasive wear behaviour of hypereutectic Al—Si—SiC composite

The microstructure, mechanical properties, and the effects of sliding distance and material removal mechanism on two-body abrasive wear behaviour of hypereutectic Al—Si—SiC composite and its matrix alloy were investigated. The hypereutectic Al—Si—SiC composite was prepared by stir casting route. The hardness, ultimate tensile strength and yield strength of the composite are increased by 17%, 38%, and 30% respectively compared with those of the matrix alloy, while the elongation of the composite is decreased by 48% compared with that of the matrix alloy. The wear rate of the materials is increased with increasing the abrasive size and the applied load and does not vary with the sliding distance. The wear surfaces and wear debris of the materials were characterized by high-resolution field emission scanning electron microscopy (HR FESEM) and wear mechanism was analyzed for low and high load regimes.     

Microstructure and shear strength of γ-TiAl/GH536 joints brazed with Ti−Zr−Cu−Ni−Fe−Co−Mo filler alloy

The influence of brazing temperature and brazing time on the microstructure and shear strength of γ-TiAl/GH536 joints brazed with Ti−Zr−Cu−Ni−Fe−Co−Mo filler was investigated using SEM, EDS, XRD and universal testing machine. Results show that all the brazed joints mainly consist of four reaction layers regardless of the brazing temperature and brazing time. The thickness of the brazed seam and the average shear strength of the joint increase firstly and then decrease with brazing temperature in the range of 1090−1170 °C and brazing time varying from 0 to 20 min. The maximum shear strength of 262 MPa is obtained at 1150 °C for 10 min. The brittle Al₃NiTi₂ and TiNi₃ intermetallics are the main controlling factors for the crack generation and deterioration of joint strength. The fracture surface is characterized as typical cleavage fracture and it mainly consists of massive brittle Al₃NiTi₂ intermetallics.     

Microstructure and properties of Cu–2.8Ni–0.6Si alloy

The phase transformation behavior and heat treatment response of Cu-2.8Ni-0.6Si (wt%) alloy subjected to different heat treatments were studied by X-ray diffraction, transmission electron microscopy observation, and measurement of hardness and electrical conductivity. The variation of hardness and electrical conductivity of the alloy was measured as a function of aging time. On aging at the temperature below TR (500-550°C) in Cu-2.8Ni-0.6Si alloy, the transformation undergoes spinodal decomposition, DO22 ordering, and d-Ni2Si phase. On aging at the temperature above TR (500-550 °C), the transformation products were precipitations of d-Ni2Si. The free energy versus composition curves were employed to explain the microstructure observations.     

Microstructure and mechanical properties of as-cast (CuNi)100−xCox medium-entropy alloys

China Foundry - Microstructure and mechanical properties of non-equiatomic (CuNi)100−xCox (x=15, 20, 25 and 30, at.%) medium-entropy alloys (MEAs) prepared by vacuum arc-melting were...