Diffusion Bonding of Ti6Al4V at Low Temperature via SMAT

Titanium alloys used to be welded to gain good joint strength at 920 °C through diffusion bonding. However, due to the heat preservation at high temperatures for a long time, we obtain joints with great bond strength while the mechanical properties of the sheet are lost. In this paper, taking Ti6Al4V alloy as an example, we studied the microstructure of the surface under the different times of surface mechanical attrition treatment (SMAT). In addition, the microstructure and mechanical properties after diffusion bonding at 800 °C-5 MPa-1 h were also conducted. The results show that the shear strength of TC4 alloy welded joint after SMAT treatment is improved, and the maximum shear strength can reach 797.7 MPa, up about 32.4%

Reactive Air Brazing of TiAl Alloy Using Ag-CuO: Microstructure and Joint Properties

TiAl alloy was successfully brazed with Ag-CuO filler in air atmosphere under simple technical conditions. The wettability of a series of Ag-CuO fillers on TiAl was analyzed. Ag-2mol%CuO filler possessed good wetting behavior on TiAl alloy. The microstructure and mechanical properties of the brazed joints were investigated. Oxide layers can be found on both sides, which can be divided into external TiO2-rich layer and internal Al2O3-rich layer. The maximum shear strength of the joint was obtained at 1020 °C holding for 20 min.

Process Influences in the Combined Compacting and Back-Injection Process to Produce Back-Injected Self-Reinforced Composites (SRCs) – Analysis via Multiple Regression Modelling

A new process to produce back-injected self-reinforced composites (SRCs) is presented. In contrast to other investigations on back-injection of SRCs, a process is presented which allows compacting and back injection of SRCs in one step where the SRCs are partly consolidated only via melt pressure inside the cavity. The mechanical properties of SRCs depend to a large extent on the process parameters of temperature and pressure during manufacture. These parameters are not yet known for back-injected areas. Sensors inside of the cavity measure the influences on the temperature and pressure conditions in the cavity. Initial studies on adhesion were carried out and analysed. For this purpose, shear tests of the back-injected component were carried out and a maximum shear strength of 5.81 MPa was determined for the materials used here. The investigations also show a dependence on the Distance from the Gate (DG) and the Mass temperature (TM). First microscopic examinations show good bonding between the SRC and the injection molded part, with no voids or air pockets in the boundary layer. It can also be seen that successful consolidation takes place in the area of the back injection.

The Mechanical Performance of Re-Bonded and Healed Adhesive Joints Activable through Induction Heating Systems

This work aims to study the healing potential properties of a reversible thermoplastic adhesive. The adhesive is activable by using induction heating systems that can induce thermal heat in the particles throughout the electromagnetic field so they can melt the adhesive for bonding or separation procedures. The healing procedure consists of damaging single lap joint (SLJ) specimens with quasi-static and fatigue tests and then using an inductor to generate an electromagnetic field able to heat the adhesive to its melting point in order to heal the damaged SLJ specimens. SLJ tests were performed on damaged and healed specimens to assess, respectively, the residual mechanical properties of the damaged specimens and the mechanical properties after healing. SLJ tests showed that the healing procedure can completely recover the joint stiffness of the damaged adhesive joints, a huge part of the maximum shear strength and the SLJ absorbed energy. This work shows also the possibility of re-bonding completely failed or separated SLJs by using the same procedure. The mechanical properties of SLJs after healing and re-bonding are compared to the SLJ compared on virgin specimens to assess the recovered mechanical properties.

Diffusion Bonding of FGH 98 and CoCrNi-Based Medium-Entropy Alloy: Microstructure Evolution and Mechanical Tests

The superalloy FGH98 was successfully diffusion bonded (DB) with medium-entropy alloy (MEA) Al3Ti3(CrCoNi)94 using pure Ni as the interlayer at a temperature range of 1050–1170 °C for 1 h under 5 MPa. The microstructure and mechanical properties of joints were investigated. The diffusion bonding seam was composed of an interlayer zone (IZ) and two diffusion-affected zones (DAZ). The IZ and DAZ beside the FGH98 consisted of cubic Ni3(TiAl)-type γ′ phases due to the diffusion of Ti and Al atoms. Meanwhile, the DAZ adjacent to the MEA consisted of spherical γ′ phases. Both of the γ′ phases with different morphology kept the coherent relationship with the matrix. Moreover, increase of bonding temperature led to the morphology of interlayer γ′ phase to transform from sphere to cube. Due to the strengthening effect of a mass of γ′ phase distributed evenly in IZ and the DAZ beside the FGH98, the microhardness and Young’s modulus of these two zones were higher than that of DAZ near the MEA. The maximum shear strength of DB joint, 592 MPa, was achieved in the joint bonded by 1150 °C, which was the typical ductile fracture feature confirmed by the shear dimples.

The Preparation of Ag Nanopaste with Silver-Plated Diamond by Low-Temperature Pressureless Sintering

Diamond/Ag nanopaste has been prepared by mixing Ag nanoparticles, silver-plated diamond particles, and an organic solvent system. Then, we characterized and studied the sintering properties of diamond/Ag nanopaste. Meanwhile, the impact factor of sintering temperature on the sintered microstructure of the diamond/Ag nanopaste on direct bonding copper (DBC) substrate was investigated. The influences of sintering temperature on the shear strength of diamond/Ag nanopaste connection layer for attaching silicon chip on the silver-plated copper substrate were analyzed. The results show that silver plating on the surface of the diamond can significantly strengthen the bonding ability between the diamond and nano-silver. When the pressureless sintering temperature increased from 150 °C to 350 °C, the porosity of diamond/Ag nanopaste decreased from 29.8% to 8.9%, and the sintered diamond/Ag joint with uniform and dense connection layer showed the maximum shear strength of 15.26 MPa as sintering at 350 °C.

Shear and tensile bond strengths of autoclaved aerated concrete (AAC) masonry with different mortar mixtures and thicknesses

Autoclaved aerated concrete (AAC) blocks are commonly used for masonry walls. In order to understand the strength of AAC masonry, it is essential to assess the tensile and shear bond strengths of the AAC block-mortar interface for various mortar combinations. This research investigates the bond strength of AAC block mortar interface made up of a) polymer modified mortar (PMM) and b) ordinary cement sand mortar of 1:4 or 1:6 ratio with thickness of 10mm, 15mm or 20mm. A thin cement slurry coating was applied on the block surface before placing the cement sand mortar in the masonry. For all types of interface, shear bond strength of masonry was studied using a triplet test, while the tensile bond strength was determined through a cross-couplet test. Among the cement sand mortar used in this study, cement sand mortar of ratio 1:4 and thickness 15mm showed the maximum shear strength of 0.13MPa with the failure of blocks as the predominant failure while the PMM had shear bond strength of 0.12MPa with the failure of blocks as the predominant failure type. However, in case of the tensile bond strength testing, PMM showed the tensile bond strength of 0.19MPa, which was highest among all the test specimens used in this study. Considering both the tensile and shear bond strengths of the AAC masonry and based on the observed failure pattern, among all the combinations used in the experiment, either PMM or cement-sand mortar of ratio 1:4 and thickness of 15mm can be chosen for the AAC masonry.

Improvement for Interfacial Microstructure and Mechanical Properties of Ti3SiC2/Cu Joint Brazed by Ag-Cu-Ti Filler with Copper Mesh

Ti3SiC2 ceramic and copper were successfully vacuum brazed using Ag-Cu-Ti filler and Ag-Cu-Ti filler with copper mesh, respectively. In this study, the effects of copper mesh and brazing parameters on the interface microstructure and mechanical properties of the joints were systematically studied. The results revealed that the typical interfacial microstructure of joint was Ti3SiC2 ceramic/Ti5Si3 + TiC + Ti2Cu + Ti3Cu/Ag (s, s) + Cu (s, s)/eutectic Ag-Cu + TiSiCu/Cu. A maximum shear strength of joint obtained at a brazing temperature of 870 °C and a holding time of 10 min can reached up to 66.3 ± 1.2 MPa, which was 34.7% higher than that without copper mesh. The improvement of mechanical property was attributed to the extraordinary plasticity of copper mesh, which reduced the residual stress caused by the difference in the coefficient of thermal expansion at the interface of joints. As the brazing temperature and holding time further increased, the shear strength of joints decreased due to the excessively thick reaction layer of intermetallic compounds.

Optimization of Process Parameters in Dissimilar Joining between SAPH 440 steel with 6061 aluminum alloy by MIG Brazing

The aim of this paper was to determine an optimal brazing condition for dissimilar joining between SAPH 440 steel with 6061 aluminum alloy. The brazing variables investigated in this study encompassed brazing speed, brazing current, wire feed rate, and torch distance and its angle. Taguchi technique was employed as the experimental strategy, and response optimizations on shear strength were performed using the S/N ratio. Results indicated that brazing variables have given a significant effect on the shear strength behavior. The optimal brazing condition was at 540mm/min of brazing speed, 25 A of brazing current, 8m/min of wire feed rate, 3mm of torch distance, and 80 degree of torch angle. Lastly, the maximum shear strength prediction of the optimal condition was 3810.50N. Confirmation tests on the optimal brazing condition were 3451.21N.