Solid-state Joints Research Articles

Applications for Solid-State Joints in the chemical process industry

Two forms of solid-state joining of tubing are explored here for use in the chemical process industry and other applications. Extrusion bonding consists of diffusion bonding an inner seamless tube of one material to an outer seamless tube of another material. Inertia welding consists of rotating one tube while pressing a second stationary tube into the first. In both cases, a very strong and robust metallurgical bond can result. This paper explores the testing and properties of such metallurgical bonds.

Processing properties of nano- and submicro-crystalline Ti–6Al–4V titanium alloy

This paper reports the results of experiments on superplastic forming (SPF) and pressure welding (PW) performed with sheets of nano- and submicro-crystalline Ti–6Al–4V alloy. The decrease in the mean grain size of Ti–6Al–4V alloy sheets from 0.4 to 0.2 μm allows the decrease of the SPF temperature from 750 to 600 °C and the fabrication of cylindrical samples with appropriate shape, bending radius and thickness distribution. Due to the low temperature superplasticity flow stress, sound solid state joint (SSJ) for nanostructured Ti–6Al–4V alloy was obtained at 600 °C. The decrease of the mean grain size to nano- and submicro-crystalline sizes allows the application of the “low temperature superplasticity” for processing hollow components out of Ti–6Al–4V alloy by combining SPF and PW.

Modeling and simulation of adaptronic drilling tool axes as the basis of control design

Drilling bars with great overhang are used for the purpose of deep drilling. Vibrations of the drilling bar and changing cutting forces based on form and position errors of a pilot hole are interrupting influences within the manufacturing process. Therefore the Fraunhofer IPT is developing an intelligent adaptronic drilling tool which enables the use of different redundant adaptronic systems each consisting of piezoactuators, solid-state joints and sensors in order to improve the accuracy of the drilling process. This paper presents the physical state-space model of the static und dynamic behaviour of one adaptronic system as the basis for further control synthesis and describes a useful tool for the multidiscipline design of the system. The starting model parameters are calculated by FEM-simulation and are fitted to measured data by an optimisation-algorithm based on Newton’s method. By describing the piezoelectric hysteresis the linear model of the mechatronic transfer behaviour is extended to a nonlinear model, which is the starting point for complex control designs for adaptronic machine tools.

Effect of heat treatment and interlayer on weld strength and microstructure of solid state joints between Cu and Al powder metallurgical preform tubes

Solid state joints made between Cu and Al powder metallurgical preforms by cold extrusion were heat treated at various temperatures and for various times with and without an interlayer (Ni) to evaluate the interfacial microstructure and weld strength. The heat treatment conditions were optimised for highest weld strength without deleterious effects in terms of intermetallic compounds, Kirkendall voids, etc. Heat treatment of these joints made without an interlayer resulted in a 40% increase in the strength. However, under some processing conditions different intermetallic compounds and phases were formed during heat treatment without an interlayer. Application of an interlayer in the form of powder allowed partial interdiffusion of metal at the interface and this minor interdiffusion had no influence on the weld strength and microstructure. Finer interlayer particle size increased the weld strength by eliminating physical discontinuities and residual particles at the interface. The heat treatment of Cu–Al joints made using 1 μm Ni powder as the interlayer increased the strength by 82% in comparison with that in the as extruded condition.

On the Model of Solid State Joint Formation under Superplastic Forming Conditions

The peculiarities of solid state joint (SSJ) formation under conditions of superplastic forming (SPF) were investigated for the titanium alloy VT6S (Ti-6Al-4V). The influence of annealing and SPF on the change of state of the alloy surface was considered. A significant role of grain boundary sliding (GBS) in the formation of both surface microrelief and SSJ was established. It was shown that SSJ formation under SPF conditions is primarily a deformation process. Corresponding schemes of the appearance of surface microrelief and SSJ formation are proposed.

Detection of weak bonding in friction welds by ultrasound

Weak bonding defects, which are special defects occurring in solid-state welded joints, are very dangerous. These defect cannot be detected effectively with normal ultrasonic testing methods used in industry, because the signal reflected from such a defect is so weak that may be overshadowed by the scattering noise from surrounding materials. In this paper, a simple model for an ultrasonic non-destructive testing of friction-welded joints, which contain joints with weak bonding defects and without any welded defect, is proposed. According to the model, it is found that the amplitude-frequency characteristic of the ultrasonic signals of the joints with various qualities is apparently different. According to the information provided by the model on the ultrasonic signals, an algorithm based on the wavelet transform is proposed. Experimental data for the friction-welded specimens show encouraging defect detection capabilities from the use of the algorithm.

Solid State Joint Formation of the Titanium Alloy VT6S under Superplastic Forming Conditions

Solid State Joint Formation of the Titanium Alloy VT6S under Superplastic Forming Conditions

Superplasticity and solid state bonding of the TiAl intermetallic compound with micro- and submicrocrystalline structure

The use of superplastic phenomenon makes it possible to reduce considerably the temperature of solid state bonding of the TiAl intermetallic compound as compared with conventional diffusion bonding. At decreasing the superplastic deformation temperature due to the reduction of the grain size an adequate decrease of the temperature threshold of solid state weldability of the TiAl intermetallic compound was observed. In the TiAl intermetallic compound with submicrocrystalline grain size the formation of a sound solid state joint occurs in the process of deformation at the temperature t = 850 C and strain {var_epsilon} = 10%. Since the temperature-strain-rate conditions of solid state bonding and those of superplasticity coincide, it is assumed that the mechanism controlling the bonding process is grain boundary sliding, the main deformation mechanism of superplasticity.

Solid State Joint Formation Under Conditions of the Process of Superplastic Forming and Diffusion Bonding

Solid State Joint Formation Under Conditions of the Process of Superplastic Forming and Diffusion Bonding

The effect of superplasticity on the solid state weldability of the titanium alloy Ti4.5Al3Mo-1V

The systematic study of solid state joint (SSJ) formation under conditions of hot and superplastic (SP) deformation by the mode of uniaxial tensile elongation and during vacuum annealing has been conducted. The two-phase VT14 alloy (Ti4.5Al3Mo-1V) with the initial microcrystalline and coarse-grained lamellar structure was taken for investigations. It has been established that deformation processes are mainly responsible for the formation of a sound joint. Annealing at the temperature of SP deformation does not increase the shear strength of joints in the samples with the initial strength of 0.4 of that of the base alloy. The considerable effect of SP deformation rate on the kinetics of SSJ formation has been revealed and it is noted that the formation of SSJ is mostly accelerated during deformation in the SP (optimum) Region II. The given experimental results show that the acceleration of sound joint formation in the SP state is attributed to the influence of grain boundary sliding (GBS), the main mechanism of SP deformation.