Maximum Efficiency Of Power Dissipation Research Articles

Dry sliding wear characteristics, corrosion behavior, and hot deformation properties of eutectic Al–Si piston alloy containing Ni-rich intermetallic compounds

Al–Si eutectic alloys could be an alternative for gray and compacted graphite cast iron engine blocks due to their excellent thermal conductivity, low density (resulting in weight reduction and fuel efficiency), and good combination of strength and ductility. However, microstructural softening at service temperature (170–250 °C) due to coarsening/coalescence of metastable precipitates and low wear resistance are a stumbling block limiting their usage in engine components. To meet endless demands for fuel-efficient car engine (i.e. higher temperature and pressure in combustion chamber), optimization of current chemical composition seems to be essential. For this reason and in the present study, different concentration of Ni (from 0.8% to 3.5%) was doped into a eutectic Al–Si alloy to investigate tribological, corrosion, and hot deformation properties. It was pointed out that Al–Si eutectic alloy containing 2–2.6% Ni had the highest wear resistance due to uniform dispersion, skeleton-type morphology of Ni-rich intermetallic compounds, and their better bonding with the matrix. Oxidation and delamination of oxide layer was shown to be the main wear mechanism. The presence of (Ni,Cu)-rich intermetallic compounds increased the corrosion rate by ≈ 60%; however, the repassivation potential was found to be slightly higher in 2.6%Ni sample indicative of easier repassivation of micropits. To better understand the high temperature behavior of Ni-containing Al–Si alloy, hot compression test was carried out within the temperature range of 400–550 °C and strain rates of 0.001 to 1s−1 and constitutive equations were used to develop hot deformation processing maps. The presence of Ni-rich intermetallic compounds enhanced the hot deformation behavior and increased the activation energy for hot deformation. Dynamic recrystallization was found to be the main softening mechanism during hot deformation. At true strain of 0.6, the maximum power dissipation efficiency (≈54%) was obtained at 400 °C and a strain rate of 0.01s−1.

Hot Deformation Behaviour and Processing Map of Cast Alloy 825

Alloy 825 is a nickel-based alloy that is commonly used in applications where both high strength and corrosion resistance are required, such as tanks in the chemical, food and petrochemical industries and oil and gas pipelines. Components made from Alloy 825 are often manufactured using hot deformation. However, there is no systematic study to optimise the processing conditions reported in literature. In this study, a processing map for as-cast Alloy 825 is established to maximise the power dissipation efficiency of hot deformation in the temperature range of 950 to 1250 °C at an interval of 50 °C and strain rate range of 0.01, {text{s}}^{ - 1} to 10.0, {text{s}}^{ - 1} to a true strain of 0.7 using a Gleeble-3500 thermomechanical simulator. The processing conditions are also correlated to the Vickers hardness of the final material, which is also characterised using optical microscopy and scanning electron microscopy, including electron backscattered diffraction. The true stress-true strain curves exhibit peak stresses followed by softening due to occurrence of dynamic recrystallization. The activation energy for plastic flow in the temperature range tested is approximately 450,{text{ kJ mol}}^{ - 1}, and the value of the stress exponent in the (hyperbolic sine-based) constitutive equation, n = 5.0, suggests that the rate-limiting mechanism of deformation is dislocation climb. Increasing deformation temperature led to a lower Vickers hardness in the deformed material, due to increased dynamic recrystallization. Raising the strain rate led to an increase in Vickers hardness in the deformed material due to increased work hardening. The maximum power dissipation efficiency is over 35%, obtained for deformation in the temperature range 1100-1250 °C and a strain rate of 0.01, {text{s}}^{ - 1}-0.1, {text{s}}^{ - 1}. These are the optimum conditions for hot working.

Hot Processing Map of an Al–4.30 Mg Alloy under High One-Pass Deformation

The high one-pass deformation behaviors of mass-produced Al–4.30Mg alloy are investigated in the temperature ranging of 350 °C–500 °C, the strain rate ranging of 0.01 s−1–1 s−1 and the reduction ranging of 50–75%. 3D processing maps are constructed by the superimposition of the instability map and the power dissipation map at the true strain of 0.69, 0.92, 1.20 and 1.38. When the true strain increases from 0.69 to 1.38, the average apparent activation energy (Q) decreases from 140.3 kJ/mol to 112.7 kJ/mol, indicating the reduction of the hot deformation energy barrier. The heating caused by a large strain of 1.38 greatly reduces the Q and improves processing efficiency. The instability regions at the strain of 0.69 appear at two domains, namely 350 °C/1.0 s−1 and 450 °C/1.0 s−1; whereas, the instability regions disappear at the strain of 1.38. The maximum efficiency of power dissipation is about 48%, which occurs at both domains of 440–480 °C/0.01 s−1/0.69 true strain and 470–500 °C/1.0 s−1/1.20 true strain. High-efficiency domains represent the optimized deformation conditions which are verified by stress-strain curves and microstructure characterization, in which the local dynamic recrystallization is observed and the power dissipates mainly by dynamic recrystallization during deformation.

The effect of Ni-doping on the microstructure, hot deformation behavior, and processing map of as-cast Al–Si piston alloy

Al–Si alloy is widely utilized in automobile pistons and cylinders due to good castability, high strength-to-weight ratio, excellent thermal conductivity, good resistance to corrosion/oxidation, and acceptable wear resistance. To increase the efficiency of engine motor, it is imperative to modify and engineer the microstructure of Al–Si alloy to enhance the high-temperature behavior. For this reason, in the current study, different concentration of Ni (0.8% and 2%) was doped into Al–Si alloy during casting to generate various Ni-rich intermetallic compounds within the alloy matrix. AlNiCu, AlCu, AlFeSi, and Mg2Si were found to be the main intermetallic compounds precipitated within the dendritic and interdendritic regions, which could enhance the thermal stability and high-temperature performance. High-temperature compression test at high temperatures ranging from 400 to 550 °C and at different strain rates ranging from 10−3 to 1 s−1 was carried out to develop high-temperature processing map and optimize the hot workability parameters of Ni-doped Al–Si alloy. The maximum power dissipation efficiency (η) was observed within the temperature range of 450–500 °C and strain rate of 0.05–0.08 s−1 (lower strain rate) for Al–Si–0.8%Ni alloy and within the temperature range of 450–500 °C and strain rate of 0.3–1 s−1 (medium to high strain rate) for Al–Si–2%Ni alloy. Dynamic recrystallization was found to be the primary softening mechanism at high temperatures (T > 450 °C).

Optimization of hot backward extrusion process parameters for flat bottom cylindrical parts of Mg-8Gd-3Y alloy based on 3D processing maps

Based on three-dimensional processing maps and numerical simulation, a demo flat bottom cylindrical part (with outer diameter of 235 mm, wall thickness of 34 mm, and height of 255 mm) of high strength Mg-Gd-Y magnesium alloy was hot backward extruded by adding an outer flange to increase the overall deformation amount and strain uniformity. Firstly, on the basis of dynamic material model and Murty instability criterion, isothermal compression stress-strain curves of cast-homogenized Mg-8Gd-3Y alloy were used to construct the processing maps. The processing maps show that the formable domain is relatively narrow: at lower strain rates ranging from 0.001 to 0.006 s−1, and the suitable temperature is from 350 to 450 °C; and at higher strain rates ranging from 0.006 to 0.1 s−1, and the temperature is from 410 to 450 °C. Then, the processing maps were integrated into a finite element software to simulate the forming process of cylindrical parts, and the influences of deformation temperature and velocity on the power dissipation efficiencies of different positions of flanged cylindrical parts were mainly discussed. The simulation results indicate that the average strain of flanged cylindrical parts reaches 30.07% and is larger than that of unflanged cylindrical parts, and the standard deviation of the strain of flanged cylindrical parts is 19.35% and less than that of unflanged cylindrical parts. The optimal process parameters corresponding to the maximum power dissipation efficiency are the temperature of 430 °C and velocity of 1 mm/s. Finally, under the optimal forming condition, the hot backward extrusion experiments of flanged cylindrical parts were conducted. The experimental results exhibit that the flanged cylindrical parts could be properly formed with good surface quality, and have relatively uniform microstructures and mechanical properties. The difference of tensile strength between the bottom and cylindrical body is less than 5 MPa, and the hardness difference is less than 1.6 HV.

Characterization of Ti-25.5Al-13.5Nb-2.8Mo-1.8Fe Alloy Hot Deformation Behavior Through Processing Map

The isothermal compression tests of Ti-25.5Al-13.5Nb-2.8Mo-1.8Fe (at.%) alloys were executed under the deformation temperature ranges of 950-1100 C with the strain rate ranges of 0.001-1 s-1, for total height reduction of 0.5. The isothermal compression deformation behavior was investigated based on flow stress curves, dynamic model analysis. The processing map of Ti-25.5Al-13.5Nb-2.8Mo-1.8Fe alloy was obtained for the optimum hot process parameters. The calculated value of Q (activation energy) was 634.5 kJ/mol. The constitutive model of the alloy was constructed. Based on DMM and the Prasad flow instability criteria, the hot processing map was established with strain of 0.7. The deformation mechanisms were interpreted by microstructural observation within both stable and instability zones. Processing map showed a stable region under the deformation temperature ranges of 950-1100 C with the strain rate ranges of 0.001-1 s-1. One certain maximum power dissipation efficiency value was approximately 43 % occurred at 950 C/0.001 s-1. Another peak power dissipation efficiency value was about 58 % at 1050 C/0.001 s-1. Both areas were the optimum processing regions. Furthermore, while the strain rate value exceeded 1 s-1, the alloy sustained deformation instability phenomenon, such as shearing band or flow localization.

Evaluation of hot deformation characteristics in modified AA5052 using processing map and activation energy map under deformation heating

The hot workability and deformation characteristics of modified AA5052 were evaluated by hot torsion testing in the temperature range 573–773 K and at strain rates of 0.1–10 s−1. Flow curves obtained from the hot torsion test were corrected considering deformation heating during hot deformation. The processing map and activation energy map were developed from this compensated flow data to propose the optimum processing conditions and to reveal the influence of hot processing parameters on microstructure evolution. The validities of the corrected processing map and activation energy map were also analyzed. The processing map showed that this alloy had a wide flow instability region at all working temperatures; in contrast, maximum power dissipation efficiency was shown at the highest and lowest strain rates in the large temperature region (above 723 K). The activation energy for hot working varied from 28 to 497 kJ mol−1 and showed a tendency for relatively small activation energy where higher power dissipation efficiency was observed. Microstructural observations indicated that dynamic recovery considerably contributed to a higher power dissipation efficiency and lower level of activation energy. On the other hand, the main reason for flow instability was attributed to the evolution of deformation bands or liquid phases. Thus, the hot deformation characteristics of the alloy proposed from the processing map and activation energy map were consistent with the deformed microstructure.

Deformation behavior of TC17 titanium alloy with basketweave microstructure during isothermal compression

The strain rate sensitivity exponent, strain hardening exponent and apparent activation energy were calculated and the processing maps of isothermally compressed TC17 titanium alloy with basketweave microstructure were established. The influence of microstructure evolution and deformation mechanisms was investigated via the high-resolution electron backscatter diffraction and transmission electron microscope. The interaction effect among globularization of alpha platelets, alpha to beta phase transformation and deformation mechanisms resulted in the different variation in strain rate sensitivity exponent at the strain rates ranging from 0.0002 s−1 to 0.1 s−1. The apparent activation energy decreased with an increase in strain and the average value was 374.3 ± 47.61 kJ mol−1. The maximum efficiency of power dissipation at 1093 K and 0.0002 s−1 was obtained and respectively reached to 0.62, 0.65, 0.56 and 0.61 at the strains of 0.1, 0.2, 0.3 and 0.4.

Processing map and microstructure evaluation of AA6061/Al2O3 nanocomposite at different temperatures

Hot compression behavior of Al6061/Al2O3 nanocomposite was investigated in the temperature range of 350–500 °C and the strain rate range of 0.0005–0.5 s−1, in order to determine the optimum conditions for the hot workability of nanocomposite. The activation energy of 285 kJ/mol for the hot compression test is obtained by using hyperbolic sine function. By means of dynamic material model (DMM) and the corresponding processing map, safe zone for the hot workability of AA6061/Al2O3 is recognized at temperature of 450 °C and strain rate of 0.0005 s−1 and at temperature of 500 °C and the strain rate range of 0.0005–0.5 s−1, with the maximum power dissipation efficiency of 38%. Elongated and kinked grains are observed at 400 °C and strain rate of 0.5 s−1 due to the severe deformation.

Analysis of hot deformation behavior and microstructure evolution of as-cast SiC nanoparticles reinforced magnesium matrix composite

Abstract

Hot Deformation Processing Map and Microstructural Evaluation of the Ni-Based Superalloy IN-738LC

Hot deformation behavior of the Ni-based superalloy IN-738LC was investigated by means of hot compression tests over the temperature range of 1000-1200 °C and strain rate range of 0.01-1 s−1. The obtained peak flow stresses were related to strain rate and temperature through the hyperbolic sine equation with activation energy of 950 kJ/mol. Dynamic material model was used to obtain the processing map of IN-738LC. Analysis of the microstructure was carried out in order to study each domain’s characteristic represented by the processing map. The results showed that dynamic recrystallization occurs in the temperature range of 1150-1200 °C and strain rate of 0.1 s−1 with the maximum power dissipation efficiency of 35%. The unstable domain was exhibited in the temperature range of 1000-1200 °C and strain rate of 1 s−1 on the occurrence of severe deformation bands and grain boundary cracking.

Constitutive and Processing Map Analyses of Stainless Steel 316 under Hot Compression

Hot deformation characteristics of stainless steel 316 were investigated at elevated temperatures. Hot compressive tests were carried out in the temperature and strain rate ranges from 800 to 1100 °C and 0.001 to 1 s1, respectively. The flow behaviors showed that the softening mechanisms were related to the dynamic recovery (DRV) and dynamic recrystallization (DRX). The constitutive equation relating flow stress, temperature, and strain rate was obtained based on the peak stress. Constitutive equation was constructed according to the hyperbolic sine constitutive law. The flow stress of stainless steel 316 was fitted well by the constitutive equation of the hyperbolic sine function. The constitutive analysis suggested that the hot deformation mechanism of the stainless steel was dislocation creep. The processing map obtained at a strain of 0.5 exhibited two domains with local maximum efficiency of power dissipation. Variation in efficiency of power dissipation was associated with the variation in ZenerHollomon parameter (Z).

Processing Map for Hot Deformation of Homogenized AZ61 Mg Alloy

Based on the experimental results from the hot compression tests of homogenized cast AZ61 Mg alloy, processing maps were constructed by superimposition of the instability maps over the power dissipation maps. The domain with the efficiency of power dissipation reaching a local maximum and flow instability region were identified in the processing maps. The processing map obtained at a strain of 0.6 exhibited only one domain with local maximum efficiency of power dissipation. The microstructure observations showed that variation in microstructure was related to the deformation condition, which was associated with the variation in efficiency of power dissipation.

The deformation instability and stability analysis of Ti-17 powder compact during thermo-mechanical processing

The deformation instability and stability of Ti–5Al–2Sn–2Zr–4Mo–4Cr (Ti-17) powder compact prepared through argon atomization and hot isostatic pressing was characterized using hot processing map. Based on hot compression experiments, the hot processing map of Ti-17 powder compact was established at temperatures from 810 °C to 920 °C and strain rates from 0.001 s−1 to 1 s−1. The deformation instability and stability regions of Ti-17 powder compact under different deformation conditions were identified. The deformation instability regions mainly focuses at temperatures from 817 °C to 927 °C and strain rates from 0.05 s−1 to 1 s−1, in which the maximum efficiency of power dissipation just reaches 0.35. The instability manifestations in adopted deformation conditions mainly are local large deformation, inhomogeneous deformation, internal crack, and deformation heating. The peak efficiency of power dissipation with the value of 0.6 in deformation stability regions corresponds to large dynamic recrystallization. The different efficiency of power dissipation in deformation stability regions could be used as a basis for selecting proper thermo-mechanical processing parameters to obtain different microstructure morphology according to the performance of the material.

Hot working of Ti-17 titanium alloy with lamellar starting structure using 3-D processing maps

Isothermal compression of Ti-17 titanium alloy with lamellar starting structure at the deformation temperatures ranging from 780 °C to 860 °C, the strain rates ranging from 0.001 to 10 s−1, and the height reductions ranging from 15% to 75% with an interval 15% were carried out. Based on experimental results, 3-D processing maps including strain were developed and used to identify various microstructural mechanisms and distinguish the safe and unsafe domains. The processing maps exhibit two maximum power dissipation efficiency domains and dynamic globularization takes place in this two domains. The first domain occurs at 800–860 °C and at strain rates lower than 0.01 s−1, and the second occurs at 780–800 °C and at strain rates lower than 0.01 s−1. With the increasing of the strains, the values of maximum power dissipation efficiency in this two domains increase. One flow instability domain due to adiabatic shear bands and lamellar kinking occurs at strain rates higher than 0.487 s−1, lower temperature, and higher strain above 0.2. The instability deformation region increases with increasing strain, strain rate, and decreasing temperature.

High-temperature deformation behavior of a gamma TiAl alloy—Microstructural evolution and mechanisms

The present investigation was carried out in the context of the internal-variable theory of inelastic deformation and the dynamic-materials model (DMM), to shed light on the high-temperature deformation mechanisms in TiAl. A series of load-relaxation tests and tensile tests were conducted on a fine-grained duplex gamma TiAl alloy at temperatures ranging from 800 °C to 1050 °C. Results of the load-relaxation tests, in which the deformation took place at an infinitesimal level (e ≅ 0.05), showed that the deformation behavior of the alloy was well described by the sum of dislocation-glide and dislocation-climb processes. To investigate the deformation behavior of the fine-grained duplex gamma TiAl alloy at a finite strain level, processing maps were constructed on the basis of a DMM. For this purpose, compression tests were carried out at temperatures ranging from 800 °C to 1250 °C using strain rates ranging from 10 to 10−4/s. Two domains were identified and characterized in the processing maps obtained at finite strain levels (0.2 and 0.6). One domain was found in the region of 980 °C and 10−3/s with a peak efficiency (maximum efficiency of power dissipation) of 48 pct and was identified as a domain of dynamic recrystallization (DRx) from microstructural observations. Another domain with a peak efficiency of 64 pct was located in the region of 1250 °C and 10−4/s and was considered to be a domain of superplasticity.

Processing maps for hot working of Cu-Ni-Zn alloys

The constitutive behaviour of α-β nickel silver in the temperature range 600–850 °C and strainrate range 0.001–100s−1 was characterized with the help of a processing map generated on the principles of the dynamic materials model. On the basis of the flow-stress data, processing maps showing the variation of the efficiency of power dissipation (given by [2m/(m+1)], wherem is the strain-rate sensitivity) with temperature and strain rate were obtained, α-β nickel silver exhibits a single domain at temperatures greater than 700 °C and at strain rates lower than 1 s−1 with a maximum efficiency of power dissipation of about 42% occurring at about 850 °C and at 0.1 s−1. In the domain, the α phase undergoes dynamic recrystallization and controls the deformation of the alloy, while the β phase deforms superplastically. Optimum conditions for the processing of α-β nickel silver are 850 °C and 0.1 s−1. The material undergoes unstable flow at strain rates of 10 and 100 s−1 and in the temperature range 600–750 °C, manifestated in the form of adiabatic shear bands.

Effect of Zirconium on the Processing Maps for Hot Working of α and α-ß Brass

The effect of zirconium on the hot working characteristics of a and α-β brass was studied in the temperature range of 500 to 850 o C and the strain rate range of 0.001 to 100 s -1 . On the basis of the flow stress data, processing maps showing the variation of the efficiency of power dissipation (given by [2m/(m+1)] where m is the strain rate sensitivity) with temperature and strain rate were obtained. The addition of zirconium to a brass decreased the maximum efficiency of power dissipation from 53 to 39%, increased the strain rate for dynamic recrystallization (DRX) from 0.001 to 0.1 s -1 and improved the hot workability

Effect of zinc content on the processing map for hot working of α brass

The hot deformation behavior of α brass with varying zinc contents in the range 3%–30% was characterized using hot compression testing in the temperature range 600–900 °C and strain rate range 0.001–100 s −1. On the basis of the flow stress data, processing maps showing the variation of the efficiency of power dissipation (given by 2m (m+1) where m is the strain rate sensitivity) with temperature and strain rate were obtained. α brass exhibits a domain of dynamic recrystallization (DRX) at temperatures greater than 0.85 T m and at strain rates lower than 1 s −1. The maximum efficiency of power dissipation increases with increasing zinc content and is in the range 33%–53%. The DRX domain shifts to lower strain rates for higher zinc contents and the strain rate for peak efficiency is in the range 0.0001–0.05 s −1. The results indicate that the DRX in α brass is controlled by the rate of interface formation (nucleation) which depends on the diffusion-controlled process of thermal recovery by climb.

Characterization of hot deformation behavior of brasses using processing maps: Part II. β Brass and α-β brass

The hot deformation behaviors of β brass in the temperature range of 550°C to 800°C and α-β brass in the temperature range of 450°C to 800°C have been characterized in the strain rate range of 0.001 to 100 s−1 using processing maps developed on the basis of the Dynamic Materials Model. The map for β brass revealed a domain of superplasticity in the entire temperature range and at strain rates lower than 1 s−1, with a maximum efficiency of power dissipation of about 68 pct. The temperature variation of the efficiency of power dissipation in the domain is similar to that of the diffusion coefficient for zinc in β brass, confirming that the diffusion-accommodated flow controls the superplasticity. The material undergoes microstructural instability in the form of adiabatic shear bands and strain markings at temperatures lower than 700°C and at strain rates higher than 10 s−1. The map for α-β brass revealed a wide domain for processing in the temperature range of 550°C to 800°C and at strain rates lower than 1 s−1, with a maximum efficiency of 54 pct occurring at about 750°C and 0.001 s−1. In the domain, the α phase undergoes dynamic recrystallization and controls the hot deformation of the alloy, while the β phase deforms superplastically. At strain rates greater than 1 s−1, α-β brass exhibits microstructural instabilities manifested as flow rotations at lower temperatures and localized shear bands at higher temperatures.