Solid State Diffusion Bonds Research Articles

Solid State Diffusion Bonding of Superplastic Duplex Stainless Steel with Carbon Steel

Solid state bonding between superplastic duplex stainless steel with carbon steel under low pressures is studied for the objectives to understand bonding behaviors and to determine mechanisms controlling bonding through the activation energy analysis. Experiments were carried out by combining several bonding parameters such as bonding temperatures, bonding pressures and surface roughness. Bond quality was evaluated by its tensile strength. Bonding strength increased with temperature, time and pressure but decreased with surface roughness. Sound bonds comparable to that of the parent metal were obtained at considerably short bonding time and low pressure. The best bonding condition obtained in this study was 1373K temperature, 3MPa pressure, 0.32μm Rmax and 220s bonding time, producing the parent metal strength with around 1% of deformation ratio. Changes in microstructures and hardness were observed across the bonding interface, due to diffusion of atoms, mainly C, from the carbon steel side to the duplex stainless steel side. A hard carburized layer formed at the DSS side and a soft decarburized layer at the carbon steel side. From the value of activation energy and experimental data, bonding was controlled mainly by two mechanisms, which were the superplastic deformation at the early stage and the diffusion of carbon at the second stage.

Microstructure of the interface of a solid state diffusion bond between Inconel alloy 718 and 17–4 PH stainless steel

The joining of dissimilar metals has widespread industrial applications, especially in the aerospace and nuclear industries [1]. It almost always causes changes or deterioration of the microstructure and mechanical properties of the original materials in the joint region. Solid-state diffusion bonding is a joining process in which the bond formation is the result of the interdiffusion of atoms across the bond interface. Owing to the fact that this is a solid state process, thus it does not suffer from such problems as segregation, cracking and distortion stresses generally encountered in liquid phase welding techniques [2]. In some cases the bond formation results in complete disappearance of the interface, and often 100% joint efficiencies can be achieved [3–5]. Diffusion bonding has emerged as a potential joining process for making precision joints between dissimilar metals.

Basic mechanisms and interface reactions in HIP diffusion bonding

The influence of interface reactions on the basic mechanisms of HIP diffusion bonding is addressed in this paper. It is shown that the mechanisms that control the microstructure and properties of solid state diffusion bonds are strongly influenced by the pre-bonding processing route used in their manufacture and by the precise chemistry of the materials being joined. In the case of precipitation hardened martensitic stainless steels the interface may be contaminated by oxide particles, which form during the early stages of the bonding process, and whose composition and morphology depend upon the chemistry of the steel. Such particles prevent grain growth across the interface and result in tensile fracture at the interface. Refinements to the pre-bonding processing route have resulted in significantly lower particle densities and grain growth across the interface. Detailed studies have revealed that under certain circumstances, HIP diffusion bonds may also be weakened by precipitation reactions or sulphur segregation at the interface during processing.

Electrode attachment, aging and thermal-cycling characteristics of yttria-based thermistors

The long-term stability of a thermistor is an important requirement for its use in industrial environments. This paper describes the testing of long-term stability of two systems, yttria–zirconia and yttria–tin oxide, with two methods of electrode attachment, solid state diffusion bonding (SSDB) and in situ lead wire attachment method (ISAM). Electrodes attached using the SSDB method show limited degradation during first few thermal cycles possibly due to the formation of microcracks. While ISAM processed Y 2O 3 samples show substantial aging behavior (resistance drift over time), Y 2Sn 2O 7 samples show very little aging. This is because Y 2Sn 2O 7 has a lower melting point than Y 2O 3 and hence sinters better leading to a denser microstructure. Thermal cycling tests conducted on the ISAM processed thermistors indicate that the assembly remains stable up to 20 cycles.

Effect of Argon Ion Bombardment on the Solid-State Diffusion Bonding of Copper

Effect of Argon Ion Bombardment on the Solid-State Diffusion Bonding of Copper

Fracture behaviour of diffusion bonded bimaterial Ti–Al joints

Failure modes of constrained metal foils between two elastic solids are rather different from those in the unconstrained condition. If the interface adhesion is strong between materials, a lower strength thin metal (plastic) foil between two much higher strength metals (elastic) can undergo substantial plastic deformation and fail with high triaxiality induced ductile fracture. Experiments have been conducted to explore the modes of failure and the factors governing fracture in such a constrained metal interlayer. In the present work, the effects of soft inter layer thickness and brittle reaction layer on the fracture behaviour of four point bend specimens have been investigated. A series of solid state diffusion bonds were produced between 25 × 25 mm section titanium bars using pure aluminium foils of different thickness (50, 457, 914, and 2000 μm) as the soft constrained inter layer. All four point bend specimens containing an ∼ 2 μm thick intermetallic reaction layer TiAl3 between the titanium and aluminium failed in ductile fracture mode within the soft aluminium interlayer next to the interface. A number of void formations were observed ahead of the crack tip next to the interface. No evidence of interface debonding was observed. However, the specimens containing an 8 μm thick TiAl3 layer failed by brittle fracture along the interface between the titanium substrate and the TiAl3 layer. It was found that decreasing the soft interlayer thickness from 2000 to 457 μm increased the load carrying capacity and decreased the fracture toughness caused by constrained plastic deformation (high triaxiality) of the interlayer.

接合中の空隙間隔分布推定手法と密着過程予測モデルの試作 固相拡散接合予測支援システムに関する研究 第１報

接合中の空隙間隔分布推定手法と密着過程予測モデルの試作 固相拡散接合予測支援システムに関する研究 第１報

Solid‐State Diffusion Bonding of Carbon–Carbon Composites with Borides and Carbides

Solid‐state diffusion bonding of carbon–carbon (C─C) composites by using boride and carbide interlayers has been investigated. The interlayer materials used in this study were single‐phase borides (TiB2 or ZrB2), eutectic mixtures of borides and carbides (ZrB2+ ZrC or TiB2+ B4C), and mixtures of TiB2+ SiC + B4C produced in situ by chemical reactions between B4C, Ti, and Si or between TiC, Si, and B. The double‐notch shear strengths of the joints produced by solid‐state reaction sintering of B4C + Ti + Si interlayers were much higher than those of joints produced with other interlayers. The maximum strength was achieved for C─C specimens bonded at 2000°C with a 2:1:1 mole ratio of Ti, Si, and B4C powders. The reaction products identified in the interlayers, after joining, were TiB2, SiC, and TiC. The joint shear strength increased with the test temperature, from 8.99 MPa at room temperature to an average value of 14.51 MPa at 2000°C.

The effect of reaction products on the fracture resistance of a metal/ceramic interface

Solid state diffusion bonds between a Ta(Ti) alloy and Al 2O 3 have been used to study the effect of reaction products on the fracture resistance of a metal/ceramic interface. The reaction layer consists of brittle intermetallics, consistent with the TiTaAl ternary phase diagram. The interface fracture energy Γ i was found to be dominated by periodic tunnel cracking of the reaction products, and was relatively insensitive to layer thickness, because of the self-similar nature of the periodic cracking. The contribution to Γ i from plastic dissipation within the alloy was minimal because the intervening reaction layer inhibited yielding. A sequence of cracking observations was used to bound the unknown values of the fracture energy of the reaction products, the residual stress within the layer and the fracture energy of the reaction product/sapphire interface.

Silicon on quartz by solid-state diffusion bonding (SSDB) technology

Silicon wafer and quartz have been successfully bonded together by a two-step thermal treatment process. SIMS measurements shows that after molecular surface activated solvent treatment, the amount of OH on the silicon or quartz surface, which is essential to the first step (low-temperature) bonding strength, is one order of magnitude higher than that on the original silicon or quartz surface. After a high-temperature (850–1250°C) solid-state diffusion process, the bonding strength between silicon and quartz is greatly increased to 150–185 kg/cm2. The material and electrical properties of the silicon on quartz substrate compares favourably with those of the bulk silicon wafer.

Factors affecting the shear strength of solid state diffusion bonds between silver-coated Clad AlZnMg alloy (aluminium alloy 7010)

Clad AlZnMg alloy (aluminium alloy 7010) sheet was argon ion sputter cleaned and ion plated with silver layers 1 μm thick and diffusion bonded in the solid state. When bonding conditions were restricted to 30 min at 220–300 °C to give 10%–15% deformation, the pressure required was 131–140 MPa. Lap shear strengths increased with increasing post-bonding solution heat treatment times to a maximum after 16 h at 480°C. For this solution heat treatment the strength increased with decrease in surface roughness but decreased with decrease in clad layer thickness. Typical shear strengths were 74–94 MPa as bonded and after solution heat treatment for 16 h they were 135–138 MPa for as-clad surfaces in the as-received condition and 156–182 MPa for clad surfaces diamond polished to a 1 μm surface finish. These strengths were significantly greater than the reported values of about 40 MPa for adhesive-bonded aluminium alloys.

Diffusion bonding and testing of Al-alloy lap shear test pieces

A quantitative measure of the effect of processing variables on the shear strength of solid state diffusion bonds is often difficult to obtain because of the scatter in test data. This may be reduced by improving the bonding and testing techniques. Two jigs for bonding and testing small Al-alloy lap shear test pieces are described. These jigs enabled the precise measurement of shear stress-strain curves for lap joints and led to reproducible shear strength values. Results obtained for diffusion bonded lap joints between clad Al-Zn-Mg (7010) alloy are described.

In situ observations of diffusion bonding using a photoemission electron microscope

The mechanisms of the later stages in the formation of solid state diffusion bonds have been investigated using a photoemission electron microscope. Mild steel specimens have been directly observed under load at temperatures up to 1000°C. The high orientation contrast of the microscope enables grain boundary movement and the annihilation of the bonding interface to be studied dynamically.