Processing map for controlling microstructure in hot working of hot isostatically pressed powder metallurgy NIMONIC AP-1 superalloy

The hot deformation behavior of hot isostatically pressed (HIP) NIMONIC AP-1 superalloy is characterized using processing maps in the temperature range 950-degrees-C to 1200-degrees-C and strain rate range 0.001 to 100 s-1. The dynamic materials model has been used for developing the processing maps which show the variation of the efficiency of power dissipation given by [2m/(m +1)] with temperature and strain rate, with m being the strain rate sensitivity of flow stress. The processing map revealed a domain of dynamic recrystallization with a peak efficiency of 40 pct at 1125-degrees-C and 0.3 s-1, and these are the optimum parameters for hot working. The microstructure developed under these conditions is free from prior particle boundary (PPB) defects, cracks, or localized shear bands. At 100 s-1 and 1200-degrees-C, the material exhibits inter-crystalline cracking, while at 0.001 s-1, the material shows wedge cracks at 1200-degrees-C and PPB cracking at 1000-degrees-C. Also at strain rates higher than 10 s-1, adiabatic shear bands occur; the limiting conditions for this flow instability are accurately predicted by a continuum criterion based on the principles of irreversible thermodynamics of large plastic flow.

Processing map for hot working of powder

The constitutive flow behavior of a metal matrix composite (MMC) with 2124 aluminum containing 20 vol pct silicon carbide particulates under hot-working conditions in the temperature range of 300 °C to 550 °C and strain-rate range of 0.001 to 1 s-1 has been studied using hot compression testing. Processing maps depicting the variation of the efficiency of power dissipation given by [2m/(m + 1)] (wherem is the strain-rate sensitivity of flow stress) with temperature and strain rate have been established for the MMC as well as for the matrix material. The maps have been interpreted on the basis of the Dynamic Materials Model (DMM). [3] The MMC exhibited a domain of superplasticity in the temperature range of 450 °C to 550 °C and at strain rates less than 0.1 s-1. At 500 °C and 1 s-1 strain rate, the MMC undergoes dynamic recrystallization (DRX), resulting in a reconstitution of microstructure. In comparison with the map for the matrix material, the DRX domain occurred at a strain rate higher by three orders of magnitude. At temperatures lower than 400 °C, the MMC exhibited dynamic recovery, while at 550 °C and 1 s-1, cracking occurred at the prior particle boundaries (representing surfaces of the initial powder particles). The optimum temperature and strain-rate combination for billet conditioning of the MMC is 500 °C and 1 s-1, while secondary metalworking may be done in the super- plasticity domain. The MMC undergoes microstructural instability at temperatures lower than 400 °C and strain rates higher than 0.1 s-1.

Thermodynamic modelling of absorption-resorption heating cycles with some new working pairs

This paper presents the results of a thermodynamic cycle analysis of single stage resorption heat pump (RHP) and resorption heat transformer (RHT) cycles with the new working pairs R22-NMP and R22-DMA. The coefficients of performance (COP) are correlated with the low grade source temperature, temperature at which useful heat is obtained and ambient temperature. The COPs are in the range 1.20–1.60 for the RHP mode and 0.25–0.45 for the RHT mode. Absorber temperatures (useful temperatures) as high as 50°C in the RHP mode and 87°C in the RHT mode have been obtained. It is observed that absorption-resorption systems are inflexible in their range of operating temperature and necessitate a higher pump work as compared with simple single-stage absorption heating systems. However, single stage RHTs show higher temperature boosts than simple absorption heat transformers.

Instability map for cold and warm working of as-cast 304 stainless steel

The deformation characteristics of as-cast 304 stainless steel under compression in the temperature range 20-600 degrees C and strain rate range 0.001-100 s(-1) have been studied with a view to characterizing the flow instabilities occurring in the microstructure. Ar strain rates of less than 0.05 s(-1), as-cast 304 stainless steel exhibits flow localization in the temperature range 20-600 degrees C, whereas dynamic strain ageing occurs at intermediate temperatures and below 5 s(-1). At room temperatures and strain rates of less than 0.05 s(-1), martensite formation is observed. To avoid the above microstructural instabilities warm working should be carried out at strain rates greater than 10 s(-1) in the temperature range 400-600 degrees C and cold working could be done in the range of about 0.05-0.8 s(-1). The continuum criterion developed on the basis of the principles of maximum rate of entropy production and separability of the dissipation function, predicts accurately all of the above instability features. (C) 1997 Elsevier Science S.A.

Processing map for the hot working of near-alpha titanium alloy 685

Using a dynamic materials model, processing and instability maps have been developed for near-alpha titanium alloy 685 in the temperature range 775-1025 degrees C and strain-rate range of 0.001-10 s(-1) to optimise its hot workability. The alloy's beta-transus temperature lies at about 1020 degrees C. The material undergoes superplasticity with a peak efficiency of 80% at 975 degrees C and 0.001 s(-1), which are the optimum parameters for alpha-beta working. The occurrence of superplasticity is attributed to two-phase microduplex structure, higher strain-rate sensitivity, low flow stress and sigmoidal variation between log flow stress and log strain rate. The material also exhibits how localisation due to adiabatic shear-band formation up to its beta-transus temperature with strain rates greater than 0.02 s(-1) and thus cracking along these regions. (C) 1997 Published by Elsevier Science S.A.

B Physics: WHEPP-XI working group report

We present the report of the B physics working group of the Workshop on High Energy Physics Phenomenology (WHEPP-XI), held at the Physical Research Laboratory, Ahmedabad, in January 2010.

Influence of homogenization on the processing map for hot working of as-cast Mg-2Zn-1Mn alloy

Processing maps have been developed for hot deformation of Mg-2Zn-1Mn alloy in as-cast condition and after homogenization with a view to evaluate the influence of homogenization. Hot compression data in the temperature range 300-500degreesC and strain rate range 0.001-100 s(-1) were used for generating the processing map. In the map for the as-cast alloy the domain of dynamic recrystallization occurring, at 450degreesC and 0.1 s(-1) has merged with another domain occurring at 500degreesC and 0.001 s(-1) representing grain boundary cracking. The latter domain is eliminated by homogenization and the dynamic recrystallization domain expanded with a higher peak efficiency occurring at 500 degreesC and 0.05 s(-1). The flow localization occurring at strain rates higher than 5 s(-1) is unaffected by homogenization.

Higgs Working Group Summary Report

Report of the Higgs working group for the Workshop "Physics at TeV Colliders", Les Houches, France 8-18 June 1999. It contains 6 separate sections: 1. Measuring Higgs boson couplings at the LHC. 2. Higgs boson production at hadron colliders at NLO. 3. Signatures of Heavy Charged Higgs Bosons at the LHC. 4. Light stop effects and Higgs boson searches at the LHC. 5. Double Higgs production at TeV Colliders in the MSSM. 6. Programs and Tools for Higgs Bosons.

Influence of working fluid on the performance of a standing-wave thermoacoustic prime mover

The thermoacoustic prime mover (TAPM) is an attractive alternative as a pressure wave generator to drive Pulse Tube Cryocoolers (PTCs), by the absence of moving parts, construction simplicity, reasonable efficiency, and environmental friendly. Decreasing the resonance frequency and improving the efficiency of the TAPM are important to drive the PTCs. These are controlled by the working gas parameters other than the dimensions of TAPM. In this technical note, the experimental studies carried out to evaluate the influence of different working fluids on the performances of a twin standing wave TAPM at various operating pressures have been compared with the simulation studies of the same system using DeltaEc wherever possible. The reasonably good agreement between them indicates the utility of DeltaEc for the optimal design of TAPM with the right working fluids for practical applications. (C) 2011 Elsevier Ltd. All rights reserved.

Transient electric field distribution within the working volume of an NEMP simulator

Nuclear electro-magnetic pulse (NEMP) simulators which are used in the simulation of transient electromagnetic fields due to a high altitude nuclear detonation are generally excited with a double exponential high voltage pulse. This results in a current distribution on the wires of the simulator and hence a transient electric field in the working volume of the simulator where the test object is kept. It is found that for the simulator under study, the current distribution is non-uniform and so is the field distribution along the width of the simulator in the working volume. To make the current distribution uniform, several methods have been suggested and the results of these methods are analyzed and suitable conclusions are arrived at from those results.