Influence of spherical particles and interfacial stress distribution on viscous flow behavior of Ti‐Cu‐Ni‐Zr‐Sn bulk metallic glass composites

Bulk metallic glass composites containing micro-scale B2 particles are subject to investigation with regards to the influence of B2 particles and interfacial stress and strain distribution on the viscous flow behavior at a super-cooled liquid state. An increased volume fraction of B2 particles leads to an increase of minimum viscosity and influences viscous flow behavior before crystallization. In high temperature deformation, the bulk metallic glass shows homogeneous deformation feature. However, the heterogeneous deformation feature is found in thermoplastically deformed bulk metallic glass composite. The strong stain accumulation and sluggish viscous flow occur around B2 particles, which are caused by the heterogeneous stress distribution linked to stress concentration and shear stress impediment around B2 particles. The sluggish viscous flow of super-cooled liquids around B2 particles during high temperature deformation induces an increase of viscosity and strongly affects the viscous flow behavior of Ti-based bulk metallic glass composites containing micro-scale spherical B2 particles.     

Welding repair of steam and gas turbine rotors made of Cr‐Mo‐V steel

Summary

An analysis is made of typical steam and gas turbine rotor failures. Based on the different causes of rotor failure and the ways in which they occur, an evaluation of the weldability of Cr‐Mo‐V steels and the classification of common turbine rotor repair possibilities are presented. The development of a specific in situ welding repair process for a damaged 20.65 MW gas turbine rotor is described. After repair, the rotor was returned to service.     

Study of prevention of solidification cracking in Al‐Mg‐Si alloy laser welds. CO2 laser welding of Al‐Mg‐Si alloys (1st report)

The choice of weld bead size in the case of welded cruciform joints can be problematic, especially when the sheets forming the joint are of differing thickness. Technological standards generally recommend a weld bead thickness less than the minimum thickness of the sheets to be joined, whereas structural standards do not envisage any dependency between joint static and fatigue strength and weld bead dimensions, unless these are so reduced as to lead to failure starting and propagating in the weld bead itself rather than the base metal plates. The scope of this study is the theoretical and experimental analysis of the change in fatigue strength with varying weld bead thickness and minimum welded plate thickness.     

Fabrication of structures by upsetting‐pressure welding

Results of investigations into the mechanical and corrosion properties and structure of friction stir welded joints in V95 alloy of the Al–Zn–Mg–Cu system are presented. It is shown that friction stir welding produces high-strength high-quality welded joints in welding of the ‘unweldable’ alloy, and the properties are determined by the condition of the heat-affected zone. It is also shown that a non-recrystallized structure forms in the core of the welded joints and the most probable mechanism of the formation of the ultrafine-grained equiaxed structure is collective dynamic polygonization and not dynamic recrystallization.     

Prospects of application of resistance‐arc cutting and treatment of metals in industry

Technological innovation of guide apparatus component restoration using the method of arc spraying by the 12Kh13+08G2S pseudoalloy is given. A submersible pump component restoration and hardening installation are designed and implemented, it includes a component surface vapour blasting unit, electroarc metallizator EM-12 and partially automated feed system for component transfer and pivoting at processing. Bench test results of the remanufactured parts showed that their wear resistance is more than twice as high.     

Increasing the load‐carrying capacity of spot welded joints in low‐carbon steels

It is shown to be possible to produce a heat-resisting coating for an intermetallic titanium alloy with the hardening ortho phase preventing changes in the surface layer of the alloy as a result of the build-up of oxide corrosion products, which can soften the component at working temperatures of 700–800°C. The results of investigation of the heat resistance properties, evolution of the composition and structure of the alloyed ion-plasma coatings on the titanium alloy with the hardening ortho-phase at working temperatures show that the deposition of the coating greatly reduces the depth in which the surface layer of the alloy changes and the thickness of this layer does not exceed 5 μm.     

Mechanism of crack propagation in multilayer deposition of wear‐resistant alloys

An analysis of the macro- and microstructure of the B95 aluminium alloy (Al–Zn–Mg–Cu system) welded joints obtained by arc, electron-beam, and mixing friction welding is carried out. Welded joints' structure and mechanical properties differences are investigated. It is shown that application of the scandium alloyed welding wire allows for preventing autocrack formation at fusion welding. The most durable and qualitative welded joints are obtained at mixing friction welding.     

Braze‐welding of electrical conductors to concentric plugs

In resistance spot welding of thin sheet–thick sheet–thick sheet joint, when the sheet thickness ratio is large (sheet thickness ratio = total thickness of sheet joint/thickness of the thin sheet positioned on the outside of the joint), how to stably secure the nugget between the thin sheet and the adjoining thick sheet is a key issue. If the sheet thickness ratio is so large, nugget formation between the thin sheet and thick sheet is extremely difficult. In order to control of the nugget (position of formation, shape, etc. of the nugget) during welding for three sheets joint with a high sheet thickness ratio, optimum welding process was investigated. The developed ‘two-step force, two-step current’ welding process was suitable for high sheet thickness ratio joint and relaxed the constraints on the sheet thickness ratio. In Step 1 (first part of welding period) of the welding process, a nugget is reliably formed between the thin sheet and thick sheet by applying conditions of low electrode force, short welding time, and high current. In the subsequent Step 2 (second part of welding period), a nugget is formed between the two thick sheets by applying high welding force and a long welding time. In the weld results of a three sheet joint (0.7+2.3+2.3 mm; sheet thickness ratio: 7.6) using mild steel GA (0.7 mm) as the thin sheet and 780 MPa high strength GA (2.3 mm) in the two thick sheets, ‘two-step force, two-step current’ spot welding process showed the wide available welding current range.     

Mechanism of hot cracking in the heat affected zone of repair welds. Repair weld cracking of service‐exposed HP‐modified heat‐resisting cast alloys (3rd report)

For several decades it has been possible to observe a tendency to light structures, particularly when they are destined to develop power and movement by consuming energy, especially when this energy derives from conventional fuel (petroleum derivates).

Lighter means of transport permit savings on fuel consumption and contribute to the environmental protection due to the reduction of greenhouse gases. The first approach in this direction had been the utilization of innovative materials able to offer further improved mechanical strength.

Nevertheless, this way presents natural limits depending on the loss of rigidity, hence excessive deformability even in the elastic field. This fact leads to the necessity to add stiffeners and reinforcing elements, but this at the same time means increase again the heaviness. Under these conditions more complex structural solutions step forward as the ‘sandwich’-structures manufacturable in a modular way provided with remarkable versatility in terms of design and choice of material. In the 1990s a European research project named ‘Sandwich’ financed by the European Union had given a significant contribution to the industrialization of structural solutions, which present a high level of innovations using aforementioned structures.

The present work proposes a preliminary study and several results of an investigation, which has as the main subject the production of innovative structural sandwich panels, in other words hybrid-sandwich panels in steel-aluminium assembled using two different joining technologies as laser and FSW, which can successively be connected as well to steel structures as to aluminium ones.     

Production of coatings of powders of self‐fluxing alloys by Shockwaves and heat treatment

The experimental results show that friction stir welding of aluminium alloys may be accompanied by the formation of defects in the form of discontinuities, delamination cavities, ‘sticking’ and also a specific ‘tunnel’ defect. The majority of these defects are associated with the welding conditions and are efficiently detected by X-ray inspection.     

The PELS‐01 microprocessor for determination of the parameters of arc welding

Summary

SCM440H steel bar to S45C steel bar welds (both of 25 mm dia.)(Part I) and SCM440H steel pipe (with an OD of 25 mm and ID of 14 mm) to S45C steel bar (of 25 mm dia.) welds (Part II) were produced, and the effect of the faying surface gradient on the properties of the friction-welded joints was investigated. The friction welding conditions were a rotational speed of 3000 rpm, preheating pressure of 20 MPa, friction pressure of 50 MPa, upset pressure of 120 MPa, and burn-off length control of 4.0 mm. Friction welding was performed with base metals with and without gradients to the faying surfaces. The results obtained may be summarised as follows.

Part I: At faying surface gradients up to 8.6/100 in the SCM base metal and up to 12.0/100 in the S45C base metal, the joints sustain tensile fracture in the S45C base metal. At any higher gradients, however, tensile fracture occurs in the weld interface. The fracture initiation point in the case of weld interface fracture is located at the periphery of the weld interface. Fractographic observations suggest that the fracture initiation zone is a dimple fracture surface containing numerous fine oxide particles in the bases of the dimples. The defect producing this type of fracture cannot be detected by ultrasonic flaw detection using the water immersion technique.

Part II: In the SCM base metal, the joints sustain tensile fracture in the HAZ of the SCM steel at a gradient up to 2.8/100. At any higher gradient, however, fracture occurs by a combination of weld interface fracture and HAZ fracture of the SCM steel. In the S45C base metal, fracture occurs in the HAZ of the SCM base metal at gradients up to 2.4/100. At gradients up to 6.0/100, the fracture behaviour found is much like that affecting SCM steel joints with a gradient. At any higher gradient, however, the joints sustain weld interface fracture.     

Optimisation of the thermal conditions of laser welding small‐diameter circular joints

The results of investigations of the effect of the strength of the magnetic field on the speed of rotation of the near-electrode areas are presented. It is shown that it is efficient to use binary hydrogen-containing mixtures for producing the gas atmosphere of the stabilized arc in plasma treatment.     

Effect of modifying additions on the ductility and plastic properties and the brittle strength of cold‐resistant,low‐alloy steel

The special features of contact-reactive soldering of crystals to the bodies of devices are investigated. The methods of soldering crystals to the bodies of power semiconductor devices with the formation of the Si–Au, Al–Zn, and Zn–Sn eutectics are analysed. New methods of lead-free contact-reactive soldering of crystals with the formation of Si–Au, Al–Zn, Zn–Sn, and Al–Zn–Sn eutectics were developed and tested.     

Effect of Ti content on TiN morphology,microstructure and toughness in coarse‐grained heat affected zone of Ti‐containing steels

It is well known that weld distortion, which has a negative influence on material properties, structural fabricability and structural integrity, should be controlled appropriately. There are many methods to control or reduce weld distortion, but most of them involve some costly process in addition to welding. In-process control of weld distortion becomes more preferable than post-welding process or other methods, when manufacturing efficiency is considered. In recent years, in-process control welding by additional cooling has been proposed as one of techniques for reducing weld distortion and partially applied for thin-plate structure in industries. However, the effectiveness of additional cooling method has not yet been fully clarified. In this study, the effectiveness of additional cooling method and appropriate cooling condition for effective reduction in weld distortion are investigated by three-dimensional thermal elastic–plastic analysis. In addition, the effect of locally cooled temperature distribution on generation behaviour of plastic strain is discussed. As a result, it is concluded that the effectiveness of additional cooling and appropriate cooling condition for reduction in weld distortion are dependent on weld distortion under consideration and welding conditions. Especially, it is necessary for reduction in weld distortion to set the cooling torch at the appropriate position. For example, in order to reduce angular distortion effectively, the appropriate cooling position is dependent on the mechanical melting length during welding.     

Energy characteristics of the power source‐welding arc system

Analytical decisions supported by experimental data were used to determine the dependences for calculating the size of the heat-affected zone (HAZ) in multilayer welding of circumferential joints in transmission gas pipelines. Data on the dimensions of this zone are essential for evaluating the possibility of applying cold cutting in the rejection of elements of gas pipelines because of defects in circumferential welded joints or welded joints in transition rings in the vicinity of circumferential welded joints.     

Numerical prediction of the microstructure of weld heat affected zone (HAZ) in SMAW weld deposits on Cr‐Mo‐V steel

It is shown that off-centre tensile loading, resulting from the presence of a convex part in one-sided butt-welded joints, has a strong effect on the stress state of welded joints leading to the formation of additional tensile stresses in the weld root.