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The nucleation and development of dynamic recrystallisation (DRX) has been studied via hot torsion testing of AISI 304 stainless steel. The DRX behaviour was investigated with microstructural analysis and slope changes of flow stress curves. The characteristics of serrated grain boundaries observed by SEM, electron backscattered diffraction and TEM indicated that the nucleated DRX grain size was similar to that of the bulged part of the original grain boundary. The DRX of the alloy was nucleated and developed by strain induced grain boundary migration and by the necklace mechanism. Before the steady state in the flow curve at 1000 ° C and 0.5 s-1, the dynamically recrystallised grains did not remain a constant size and gradually grew to the size of fully DRX grains at steady state (30 μm). The calculation of the grain size was based on X DRX (volume fraction of dynamically recrystallisation) under the assumption that the nucleated DRX grains grow to the steady state continuously. It was found that...

The high-temperature deformation behavior and dynamic softening transition from dynamic recrystallization (DRX) to dynamic recovery (DRV) of Al-18 wt.%Si alloy was studied by torsion tests in a temperature range of 573∼773 K and a strain rate range of 0.001∼1/sec. The alloy was produced by spray-forming followed by hot extrusion. The dependence of flow stress (σ) on strain rate $$(\dot \varepsilon )$$ and temperature (T) could be described by the power Arrhenius relationship, $$\dot \varepsilon = A \sigma _p^n exp( - Q/RT)$$ . The activation energy and stress exponent values were higher at the low temperature region than those at the high temperature region. The alloy showed a flow curve of DRX in the temperature range of 573∼673 K, while at 673∼773 K, the alloy exhibited a flow curve of DRV. These results were analyzed by observing the shapes of the flow curves throughout the deformation condition. Also, the transition behavior from DRX to DRV has been investigated through observation of deformed microstructure and flow curves during hot deformation.

The high temperature deformation behavior of Al 6061 composites reinforced with SiC and Al2O3 particles has been studied in the temperature range of 300–550°C and the strain rate range of 0.1–3.0/sec by hot torsion test. The deformation efficiency η, given by (2m/m + 1), where m is the strain rate sensitivity, is calculated as a function of temperature and strain rate to obtain iso-efficiency contour map. The composite reinforced with SiC particle exhibited a domain of dynamic recrystallization (DRX) with a peak efficiency of ∼40% at the temperature range of 450–500°C and strain rate range of 0.2–0.5/sec. On the other hand, the composite reinforced with Al2O3 particle showed the DRX domain at the temperature range of 450–480°C and strain rate range of 0.1–0.2/sec. The characteristics of these domain have been investigated with the help of microstructural observation and hot ductility measurements.

Hot deformation has been carried out for AA 2024 composites reinforced with 1 and 8 μm SiCp (15 vol. %) to suggest optimum hot working condition for DRX at the temperature range of 320 to 520 °C and strain rate range of 0.1 to 3.0/sec. Processing maps showing the variation of the efficiency of power dissipation expressed by [2m/(m+1)], where m is the strain rate sensitivity, with temperature and strain rate have been described for the composites. The characteristics of domain of dynamic recrystallization (DRX) and peak efficiency of the composites have been analyzed by observing deformed microstructure. The SiCp/AA 2024 composite with 8 μm SiCp showed 40 ∼ 50 % efficiency at the DRX domain (370∼460 °C, 0.1∼0.5/sec). Also, the variation of deformation efficiency with Zener-Hollomon parameter (Z=e exp(Q/RT)) were discussed to find out optimum hot working condition for the composites. It is found that the optimum temperature and strain rate condition for DRX of the composites is 430-450 °C and 0.5/sec.

Hot torsion test has been carried out for Al 2024 composite reinforced with 8 μm SiCp (15 vol.%) to suggest optimum hot working condition for dynamic recrystallization (DRX) at the temperature range of 320 to 520 °C and strain rate range of 0.1 to 3.0/sec. Flow curve and deformed microstructure have been analyzed to identify the hot restoration mechanism of DRX. Processing map showing the variation of the deformation efficiency expressed by [2m/(m + 1)], where m is the strain rate sensitivity, with temperature and strain rate has been described for the composite. The characteristics of domain of DRX and peak efficiency of the composite have been analyzed by observing deformed microstructure. The composite showed 40–50% efficiency at the DRX domain (370–460 °C, 0.1–0.5/sec). Also, the variation of deformation efficiency with Zener-Hollomon parameter (Z = έ exp(Q/RT)) were discussed to find out optimum hot working condition for DRX of the composite. It is found that the optimum temperature and strain rate condition for DRX of the composite is 430–450 °C and 0.5/sec.

The dynamic deformation behavior of Al 2024 composites reinforced with 1 and 8 µm SiCp (15 vol.%) has been investigated in the temperature range of 370 to 500°C and strain rate range of 0.1 to 3.0/sec by torsion testing. Processing maps showing the variation of the efficiency of power dissipation expressed by [2m/(m+l)], where m is the strain rate sensitivity, with temperature and strain rate have been described for the composites. Also, the domain of dynamic recrystallization (DRX) and peak efficiency of the composites were analyzed to suggest an optimum hot working condition for DRX. The SiCp/A12024 composite with 8 (µm SiCp showed 40% efficiency at the DRX domain (370~460°C, 0.1~0.5/sec). The optimum temperature and strain rate condition for the DRX of the composites is 430~450°C and 0.5/sec. The characteristics of these results were discussed with the help of microstructural observation during hot deformation.

The hot workability of AA 2024 composites reinforced with different volume fractions (5, 10, 15, 20, and 30 vol%) of SiCp was investigated within the temperature range 320–500°C at a strain-rate of 1.0 s−1. Dynamic recrystallization (DRX) or dynamic recovery (DRV) of the composites was studied from the flow curves and deformed microstructures. The effect of the SiCp volume fraction on the critical strain for the onset of DRX was analyzed from the relationship between the work-hardening rate and effective strain during hot deformation. The addition of the SiCp to an AA 2024 matrix alloy increased the dislocation density, resulting in a high flow stress and a low critical strain for the DRX of the composites. Upon increasing the SiCp volume fraction, the flow stress and the temperature showing the highest failure strain increased. Also, the difference in flow stress amongst the composites decreased with increasing deformation temperature. This result has been discussed in relation to dislocation density and stacking fault in the matrix of the composites.

The hybrid composites with different ratios of SiC w and SiC p (SiC w : SiC p =1:1, 1:2, and 1:3) were fabricated by the powder-metallurgy route and were solution treated followed by aging treatment. Mechanical properties of the hybrid composites reinforced with both SiC whiskers (SiC w ) and SiC particles (SiC p ) were investigated. The peak aging time for the hybrid composites was determined from the measurement of matrix hardness. Accelerated aging occurred in the hybrid composites and the peak aging time (∼5 h) was similar in all the hybrid composites. The hybrid composite with SiC w : SiC p =1:1 showed the highest ultimate tensile strength. The work hardening rate of under-aged hybrid composite with SiC w : SiC p =1:1 was higher than that of over-aged one.

The hot-deformation behaviour of AA2124 composites reinforced with both whiskers and particles of silicon carbide (15 vol% SiC w + SiC p ) was investigated by means of hot torsion tests in the temperature range 300 to 500 °C over a strain rate range of 1.32 × 10 −3 to 2.38 s −1 . The composites with various SiC w : SiC p ratios of 1:1, 1:2 and 1:3 were fabricated by the powder-metallurgy route. From the flow curves and hot-deformed microstructures, the hot recovery mechanism of composites deformed at 300–400 °C at 1.32 × 10 −3 s −1 strain rate was found to be dynamic recrystallization, while at temperatures higher than 450 °C dynamic recovery was responsible for the hot recovery mechanism of the composites. It was found that the composite with SiC w :SiC p = 1:1 showed the highest flow stress (52 MPa) and failure strain (375%) at 450 °C and 7.94 × 10 −2 s −1 .

A computationlly efficient Cartesian path generation algorithm is proposed. The proposed tool path generation procedure is essentially a two-step process. The first step subdivides the sculptured surface into subpatches until the subdivision is good enough to satisfy the user-defined approximation tolerance. The second step generates the Cartesian tool paths from the polyhedral approximation of the surface while the deviation of the tool paths from the true surface stays within the user-specified tolerance. This algorithm optimizes the cutter movements by minimizing the number of interpolated points. The Cartesian tool path generation procedure is implemented in C on a SUN 4/65 workstation as a module in an integrated sculptured surface design and manufacturing (ISSDM) system.