WARM DEFORMATION BEHAVIOR OF A 65MN SPRING STEEL

The warm deformation behavior of 65Mn spring steel has been carried out by a thermomechanical simulator. The deformation temperatures are in the range of 550 ~ 700℃ and strain rates are in the range of 0.001 ~ 1 s-1. The deformation activation energy is calculated to be 486.829 KJ•mol-1. The strain compensated Arrhenius-type constitutive model was established. The relationship materials constants and strain were fitted with an 8th order polynomial. It was found that the strain has a significant influence on the instability map. At the strain is 0.3, the optimum flow zone may take place with the deformation temperatures higher than 626 ℃ and strain rate in the range of 0.001 ~ 1 s-1.

Effect of Different Fuels On Combustion Instabilities in an Annular Combustors

Combustion instability in annular combustors of jet engines is a recurring issue. In the present study, the characteristics of instabilities for different fuels are investigated by combining the instability maps obtained in a laboratory-scale annular combustor equipped with multiple swirling spray injectors (MICCA-Spray) and flame describing functions (FDFs) from a single sector configuration (SICCA-Spray). Two types of liquid fuels are injected as hollow cone sprays: heptane, which is fairly volatile, and dodecane, which is less volatile. Experiments are also conducted with gaseous propane, premixed with air, which serves as a reference. An instability map is systematically drawn by varying the global equivalence ratio and thermal power. The data indicate that the amplitude and frequency of instabilities depend, for the same operating point, on the fuel injection conditions and fuel type. Overall trends show that premixed propane is unstable in a broad operating domain. Injection of liquid fuels induce changes in flame time lag that modify the unstable regions. For heptane, the instability map is closer to the propane reference map, whereas dodecane exhibits wider stable regions. An attempt is made to understand these features by examining the FDF, which gives the ratio of relative fluctuations in heat release rate to the relative fluctuations in velocity. The FDFs measured in a single sector configuration give access to gain and phase information that can be used to determine unstable bands and calculate an instability index guiding the interpretation of the differences in instabilities of the three fuels.

Hot Deformation Treatment of Grain-Modified Mg–Li Alloy

In this work, a systematic analysis of the hot deformation mechanism and a microstructure characterization of an as-cast single α-phase Mg–4.5 Li–1.5 Al alloy modified with 0.2% TiB addition, as a grain refiner, is presented. The optimized constitutive model and hot working terms of the Mg–Li alloy were also determined. The hot compression procedure of the Mg–4.5 Li–1.5 Al + 0.2 TiB alloy was performed using a DIL 805 A/D dilatometer at deformation temperatures from 250 °C to 400 °C and with strain rates of 0.01–1 s−1. The processing map adapted from a dynamic material model (DMM) of the as-cast alloy was developed through the superposition of the established instability map and power dissipation map. By considering the processing maps and microstructure characteristics, the processing window for the Mg–Li alloy were determined to be at the deformation temperature of 590 K–670 K and with a strain rate range of 0.01–0.02 s−1.

Effect of Different Fuels on Combustion Instabilities in an Annular Combustor

Combustion instabilities in annular combustors of jet engines is a recurring issue. In the present study, the characteristics of instabilities for different fuels are investigated by combining the instability maps obtained in an annular combustor equipped with multiple swirling spray injectors (MICCA-Spray) and flame describing functions (FDFs) from a single sector configuration (SICCA-Spray). Two types of liquid fuels are injected as hollow cone sprays: heptane, which is fairly volatile, and dodecane, which is less volatile. Experiments are also conducted with gaseous propane, perfectly premixed with air, which serves as a reference. An instability map is systematically drawn by varying the global equivalence ratio and thermal power. The data indicate that the amplitude and frequency of instabilities depend, for the same operating point, on the fuel injection conditions (premixed or spray) and fuel type. Overall trends show that premixed propane is unstable in a broad operating domain. Injection of liquid fuels induces changes in time lag that modify the unstable regions. For heptane the instability map is closer to the propane reference map whereas dodecane exhibits wider stable regions. Variations can also be observed in the behavior of spin ratio that characterizes the azimuthal structure of the coupling mode. An attempt is made to understand these features by examining the FDF, which gives the ratio of relative fluctuations in heat release rate to the relative fluctuations in velocity. The FDFs measured in a single sector configuration gives access to gain and phase information that can be used to determine unstable bands. It is found that based on whether the MICCA-Spray instability frequency is within these bands, the instability amplitude can be high or low. This indicates that the difference in instabilities between the three fuels can be linked to the variations in FDFs.

Development of Processing Map for Superplastic Deformation of Ti-6Al-4V Alloy

A processing map plays a major role in indicating safe and failure regions of a process conducted in a hot working regime. It also shows the response of a material, by indicating changes in the microstructural evolution through temperature. In the present study, a processing map has been developed depending on the flow stress data of Ti-6Al-4V alloy sheet in a strain rate range of 10−2 /s to 10−4 /s and over a temperature range of 700°C to 900°C in order to identify the presence of superplasticity region. The flow stress data have been acquired on the basis of temperature, strain and strain rate by conducting hot uniaxial tensile tests. Based on this, a power dissipation map is obtained to show the percentage of efficiency, as it is directly related to the amount of internal entropy produced. In addition, an instability map is also obtained, as it identifies the flow instability that are to be avoided during hot working process. Finally, a processing map has been established by overlaying instability map on efficiency map. The results clearly reveal that the superplastic deformation occurs within a temperature range of 750°C to 900°C at a strain rate of 10−4 /s, without any flow instability in this region.

Microstructure Mapping: An Approach to Quantitative Interpretation of Microstructural Evolution in Indian Fast Reactor Advanced Clad Material during Hot Forging

In this paper, microstructural evolution of Indian Fast Reactor Advanced Clad (IFAC-1) steel during thermo-mechanical processing has been investigated. Hot isothermal forging has been simulated in a Gleeble® thermo-mechanical simulator in the temperature range 1173-1473K and true strain rate range 0.01-100s-1. Instability map has been developed using the stress-strain data obtained. Effect of major forging parameters on various microstructural features has been studied quantitatively. Results from this study have been used to construct various maps (‘μ-maps’) representing different aspects of microstructural evolution. An analogy between the μ-maps and instability maps provides essential insights into possible instability mechanisms operative in the material. The μ-map analysis shows potential as a tool for optimisation of industrial-scale forging parameters.

Hot Deformation and Processing Maps of 7005 Aluminum Alloy

The deformation behavior of 7005 alloy was studied by hot compression tests. The processing map was constructed by superimposing the instability map over the power dissipation map at a strain of 0.7 using the corrected flow stress data to eliminate the effect of friction. Microstructural examination was performed for validation. It can be found that the flow stresses increase with the decrease of deformation temperature or the increase of strain rate. At the relatively high strain rates, the material exhibits flow instability manifesting as adiabatic shear bands or flow localization. A large volume of coarse precipitations distributing in the grain boundaries in one of the peak efficiency domains: 275–325 °C/0.0005–0.001 s−1, which may result in inter-granular corrosion and spalling layer, should be avoided in the final deformed alloy. The optimum hot working domain is the temperature range of 400–450 °C and strain rate range of 0.0005–0.005 s−1, at which DRX is identified.

Processing Map of Mg-13Al-3Ca-3Zn-1Nd-0.2Mn Magnesium Alloy

Compression tests of Mg-13Al-3Ca-3Zn-1Nd-0.2Mn Magnesium alloy as-extruded had been performed in the compression temperature range from 200°C to 400°C and the strain rate range from 0.001 s−1 to 10 s−1 and the flow stress data obtained from the tests were used to develop the power dissipation map, instability map and processing map. The most unsuitable zones in the power dissipation map including 200°C - 315°C and 0.01s-1- 0.1s-1 zone, 315°C - 400°C and 0.001s-1- 0.01s-1zone and 340°C - 360°C and 0.32 s-1- 0.56 s-1zone. The most unsuitable zones in the instability map are 310°C - 400°C, 0.001s-1to 0.56 s-1zone and 330°C - 400°C, 1s-1to 10 s-1zone. The most suitable temperature range is 330°C - 400°C and most optimal strain rate ranges are 1 s-1- 10 s-1and 0.001s-1- 0.56 s-1.