3D Transient Thermal Modelling and Experimental Validation of the Temperature Distribution During Laser Heating of Ti6Al4V Alloy

Abstract. A three 3D transient finite element model has been developed to predict the temperature distribution in Ti6Al4V alloy plate workpiece. It is found that the temperature profile is strongly dependent on the parameters of the laser beam and material properties. Also the thermal model results were compared with results produced by experimental work and these show close agreement

Directionally structured dual phase steel composites

Manganese partitioning and mechanical properties of dual phase steels have been examined. The manganese partitioning coefficient increases to a limit with increasing isothermal holding time, and the final equilibrium partitioning coefficient decreases with increasing annealing temperature. The combination of diffusion equations in austenite and ferrite plus mass balance and austenite growth can give the manganese distribution in austenite and ferrite respectively, and the manganese partitioning coefficient at any isothermal holding time. The introduction of rolling during annealing or at the end of annealing can strengthen dual phase steels by elongating austenite and introducing internal stresses and dislocations, the magnitude of which depends on finishing rolling temperature and the timing of rolling during annealing. The tensile properties of as-rolled dual phase steels are strongly influenced by finishing rolling temperature and martensite volume fraction because of internal stresses and dislocation density, whereas those of post-rolling annealed steels depend on only martensite volume percentage. To model the heat-treatment for producing dual phase steels (“in-situ” dual phase steel), a steel-steel composite is produced by incorporating high strength steel-wires into ductile steel sheets through hot-rolling (“artificial” dual phase steel). The properties of the reinforcing wire, matrix steels, interfacial strength between wire and matrix steels and steel-steel composite are affected by the surface condition of wire, finishing rolling temperature, preform holding time at rolling temperature before rolling, and heat-treatment after fabrication of composites. Mileiko’s theory can predict the relationship between the steel-steel composite strength and the volume fraction of wire. But for dual phase steels, Mileiko’s theory can be applied only when martensite volume fraction is over 30% because the residual stress, high dislocation density and carbide are produced at low temperature, at which low martensite volume fraction is obtained. Continuous wire composites can simulate the as-rolled dual phase steel when the reinforcement content is over 30%, but discontinuous wire composites can not simulate the post-rolling annealed dual phase steel

Structures and residual stresses of Cr fibers in Cu-15Cr in-situ composites

The substructures of Cr ribbon/fibers in Cu-15Cr in-situ composites under both the as-drawn and aged conditions have been examined by transmission electron microscopy (TEM) observation. The residual stress in the axial direction of the deformed Cr ribbon/fiber has been evaluated by X-ray diffraction. Deformation strain partitioning between Cu and Cr phases occurs during cold drawing because of large differences in modulus and flow stress between Cu and Cr. The axial residual stress in the Cr fibers does not increase significantly with further cold drawing after the preferred orientation of the Cr phase has been fully developed (drawing strain > 4.5), because dynamic recovery and recrystallization of the fcc Cu minimize the misfit strain between the Cr fibers and the Cu matrix. The compressive axial residual stress in the Cr fibers is produced by aging treatments at temperatures above 580°C because of the large difference in thermal expansion coefficient between Cu and Cr

Fabrication and mechanical properties of steel-steel composites

Metal matrix composites based on a low carbon steel matrix reinforced with high carbon steel wires have been fabricated by a combined cold and hot rolling process. Both continuously and discontinuously aligned composites have been produced. A subsequent heat treatment allowed the formation of martenisitc, bainitic or pearlitic wires in a ferrite predominantly matrix. The optimum wire microstructure giving a composite with high strength and reasonable ductility was found to be bainitic — martensitic wires were found to contain microcracks that gave poor composite strengths and ductilities. The discontinuous wire composites produced similar strengths to the continuous composites only when they were deformed to give a wire aspect ratio greater than 20. The strengths of both types of composites showed a good fit to the rule of mixtures as the volume fraction of fibers was increased

Interfacial properties in steel-steel composite materials

Steel–steel composites comprising low carbon steel reinforced with eutectoid steel wire have been fabricated by rolling to simulate the character of dual-phase steels. The interfacial strength of these steel–steel composites and its influence on mechanical properties has been examined. Analysis based on the energy equilibrium that the work of interfacial shear fracture equals the total energy of the bonds broken during wire pull-out has been developed and shows that the interfacial strength is mainly affected by the distortion of the interface and carbon diffusion between matrix and wire

Properties of thermomechanically processed dual-phase steels containing fibrous martensite

Manganese partitioning and long fibrous martensite were obtained in several dual-phase steels by annealing, followed by hot rolling in their respective intercritical annealing temperature regions. The volume fraction of martensite was varied by changing the intercritical annealing temperature. Long annealing times were required to obtain complete manganese partitioning in order to increase the strength of the austenite phase and subsequently the martensite phase. Post-roll annealing improves the ductility through ferrite recrystallisation and also by changes to the martensite morphology, however, this results in a decrease in strength. The as-rolled steel shows two distinct work-hardening processes with different exponents and shows a laminated fracture appearance due to the ribbon-like morphology of the martensite

Comparison between continuous wave and pulsed Nd: YAG laser cladding of stellite 6

Abstract not available

Effect of laser beam on the chip formation in machining of titanium alloys

The effect of laser beam on chip formation when machining Ti6Al4V alloy has been investigated at different cutting speeds, laser power and tool-beam distance. The characteristics of the segmented chip produced by laser assisted machining (LAM) in terms of the tooth depth and tooth spacing are strongly dependent on the cutting speed, laser power and tool-beam distance. Two types of segmented chip were formed, one at low and the other at high cutting speeds respectively with the continuous chip occurring between these two types of segmented chips. The critical cutting speed at which the transition from the sharp, segmented chip to the continuous chip occurs increases with laser power and strongly depends on the tool-beam distance. The chip becomes sharper with increasing cutting speed. To obtain the continuous chip, plastic deformation near the free surface to match the deformation strain by the cutting tool is required, which can be achieved by laser pre-heating the material in front of the cutting tool

Effect of tool wear on chip formation during dry machining of Ti-6Al-4V alloy, part 2: effect of tool failure modes

Variation in the geometric and surface features of segmented chips with an increase in the volume of material removed and tool wear has been investigated at cutting speeds of 150 and 220 m/min at which the cutting tools fail due to gradual flank wear and plastic deformation of the cutting edge, respectively. Among the investigated geometric variables of the segmented chips, slipping angle, undeformed surface length, segment spacing, degree of segmentation and chip width showed the different variation trends with an increase in the volume of material removed or flank wear width, and achieved different values when tool failed at different cutting speeds. However, the chip geometric ratio showed a similar variation trend with an increase in the volume of material removed and flank wear width, and achieved the similar value at the end of tool lives at cutting speeds of both 150 and 220 m/min regardless of the different tool failure modes. Plastic deformation of the tool cutting edge results in severe damage on the machined surface of the chip and significant compression deformation on the undeformed surface of the chip