Increasing Compression Temperature Research Articles

Hot compressive deformation and microstructural evolution of 60NiTi alloy

Hot deformation behavior and microstructure of 60NiTi alloy during hot compressive deformation were investigated using Gleeble−3500 thermal simulation test machine in the temperature range of 500−650 °C and strain rate range of 0.001−1 s−1. The constitutive equation of hot compression was constructed and the hot processing maps were plotted. When the compression temperature rose or the strain rate declined, the peak stress reduced. The hot deformation activation energy was calculated as 327.89 kJ/mol, and the proper hot working parameters of compression temperature of 600−650 °C and strain rate of 0.005−0.05 s−1 were obtained. The recrystallization degree increased with increasing compression temperature. When the strain rate increased, both dislocation density and number of twins were improved, and the Ni3Ti phase tended to aggregate. Ni3Ti precipitation phase was beneficial to inducing dynamic recrystallization of the 60NiTi alloy. The dynamic recovery, dynamic recrystallization and twinning took place during hot compressive deformation of the 60NiTi alloy.

Roughness, wettability, and morphological properties of impregnated and densified wood materials

The effects of pre-impregnation on surface roughness, wettability, and morphological structure of densified aspen and fir wood were investigated. Wood specimens were impregnated with paraffin, linseed oil, and styrene after pre-vacuum treatment. The impregnated specimens were densified using compression ratios of 20% and 40% at 120 °C, 150 °C, and 180 °C. The roughness decreased and the contact angle increased in all impregnated specimens (undensified and densified). Compared to paraffin and linseed oil-impregnated specimens, lower roughness and higher contact angle were found in styrene-impregnated specimens. After densification, the roughness and wettability of the wood specimens decreased. More successful results (lower roughness and higher contact angle) were generally obtained in specimens densified with high compression ratio (40%). In both untreated and impregnated specimens, the contact angle increased with increasing compression temperature. While the effect of compression temperature on the roughness of the fir specimens was not significant, the roughness of the aspen specimens (especially styrene-impregnated) decreased with the increase in temperature. Scanning electron microscopy observations indicated that impregnation agents (especially styrene) clung to wood cell walls and partially or completely filled the lumens. This was positively correlated with the determined roughness and wettability. Pre-impregnation facilitated wood densification without significant cell deformations.

Deformation behavior, microstructure evolution, and dynamic recrystallization mechanism of an AZ31 Mg alloy under high-throughput gradient thermal compression

A high-throughput gradient thermal compression process was adopted to investigate the effects of thermal deformation parameters on the deformation behavior and microstructure evolution of a rolled AZ31 Mg alloy. The results showed that with increasing deformation degree, the flow stress-strain curves of the double-cone samples compressed along the normal direction (ND), transverse direction (TD), and rolling direction (RD) of rolled Mg alloy rapidly reached their peak value, then decreased gradually, and finally maintained a trend of horizontal change. Under the same strain condition, the dynamic recrystallization (DRX) degree of the double-cone sample increased gradually with increased deformation temperature. Twins were more likely to occur when compression occurred in the TD and RD, rather than along ND. With increasing temperature or strain, the number of twins that formed during compression gradually decreased. At deformation temperatures of 250 °C and 300 °C, continuous dynamic recrystallization was the main DRX mechanism in the double-cone samples compressed along the ND, TD, and RD. Furthermore, the twin-assisted DRX mechanism also occurred in the double-cone samples compressed at 250 °C along the TD and RD. During compression at 350 °C and 400 °C along the ND, TD, and RD, discontinuous dynamic recrystallization occurred in the double-cone samples, indicating that the DRX mechanism changed with increasing compression temperature.

Deformation microstructure and thermomechanical processing maps of homogenized AA2070 aluminum alloy

The hot deformation behavior of homogenized AA2070 Al–Li–Cu alloy was studied using isothermal compression in a temperature range of 300 °C–500 °C and a strain rate range of 0.001 s-1 to 1 s-1. Deformation microstructure was characterized using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) including weak beam dark field STEM imaging to correlate the microstructure evolution with hot deformation mechanism. TEM/STEM results show that a high density of fine T1 (Al2LiCu) phase forms in the microstructure through dynamic precipitation at compression temperatures lower than 400 °C, especially at low strain rates. Constitutive analysis shows that back stress due to dynamic precipitation of T1 phase decreases with increasing compression temperature and increasing strain rate. EBSD characterization indicates that dynamic recovery is the main softening mechanism at temperatures below 400 °C. At 400 °C and above, intermetallic phases including T1, Al20Cu2Mn3 and Al3Cu2 in the microstructure gradually dissolve, and dynamic recrystallization becomes the dominant softening mechanism, resulting in texture weakening and grain refinement. Three dynamic recrystallization mechanisms including discontinuous dynamic recrystallization (DDRX) at large angle grain boundaries, particle stimulated nucleation (PSN) and continuous dynamic recrystallization (CDRX) were observed. Based on hot work efficiency, deformation instability and microstructure evaluation, processing maps were constructed using both conventional method and Garofalo sinh equation, providing optimum processing conditions (temperature >400 °C and strain rate <0.1 s-1) for industrial forging, extrusion and rolling processes.

Effect of deformation parameters in unrecrystallization range on microstructural characteristics in Al-bearing hot-rolled TRIP steel

The scanning electron microscope, transmission electron microscope, optical microscope, X-ray diffraction and hardness tests were used to investigate the effect of deformation parameters in unrecrystallization range on microstructural characteristics in Al-bearing hot-rolled transformation-induced plasticity steel. The thermomechanical-controlled processing was carried out with thermomechanical simulation machine, and the samples were compressed to compression strains of 0, 0.15, 0.25 and 0.35 at compression temperatures of 850, 900 and 950 °C. The results showed that the volume fraction of polygonal ferrite increased with the increasing compression strain, while the volume fraction of retained austenite reached the maximum value at compression strain of 0.25. The volume fraction of polygonal ferrite decreased with the increasing compression temperature, whereas the volume fraction of retained austenite possessed the maximum value at compression temperature of 850 °C. Some granular retained austenite was present in uncompressed samples, and some pearlite appeared at large compression strain, while the hardness of the samples exhibited the similar variation tendency to the volume fraction of retained austenite.

Microstructure and texture evolution near the adiabatic shear band (ASB) in TC17 Titanium alloy with starting equiaxed microstructure studied by EBSD

The microstructure and texture evolution near the adiabatic shear band (ASB) in TC17 Titanium alloy, during hot compression, were studied by electron back-scattered diffraction (EBSD). The ASB was induced in the bulk cylindrical TC17 Titanium alloy with an initially equiaxed microstructure, by hot compression with a relatively low strain rate. When the equiaxed-microstructure TC17 Titanium alloy was compressed at 600 °C, 700 °C, and 850 °C, two kinds of ASB were observed: D-ASB, which is almost parallel to the diagonal of the longitudinal section, and H-ASB, which is almost parallel to the horizontal of the longitudinal section. Dynamic recrystallization took place in β phase grains at the ASB center, while dynamic recovery dominated at the transition region. The large angle grain boundaries (LAGBs) were mainly concentrated in β phase, while the small angle grain boundaries (SAGBs) were mainly concentrated in α phase distributed along the ASB direction. Meanwhile, both α and β phase grain sizes slightly increased with increasing hot compression temperature and deformation, except for the alloy compressed at 850 °C with 70% deformation due to the phase transformation. At the ASB center, prismatic textures existed in α phase grains except for the basal textures in the alloy deformed at 600 °C. In β phase grains, the {001} planes were always normal to CD, while the {111} planes were normal to CD in the initial microstructure of the TC17 alloy. Furthermore, in β phase grains, the cubic texture {100} 〈001〉 dominated in the TC17 alloy deformed at 600 °C, 700 °C, and 850 °C. With increasing compression temperature, the crystal plane parallel to the ASB direction in α phase grains changed from {0001} to {112¯0} while it was stable in β phase grains, which is not beneficial to the mechanical performance of this alloy.

Fixation of Soft-inner Part of Oil Palm Trunk by Close System Compression Method

Compression by closes system compression (CSC) improved quality of the soft-inner part of oil palm trunk (S-OPT). The problem of compressed-wood was spring back or recovery of set, if it was exposed to moisture content. The objective of these study were to evaluate the recovery of set (RS) and weight loss (WL) of S-OPT by CSC. These methods were compared with heat treatment (HT) and steam treatment (ST). Density of S-OPT was 0.3 g/cm3. All samples were compressed to compression ratio of 50%. The compression of HT method used the temperatur of 120, 140, 160, 180 and 200 °C for 0, 10, 30, 60 and 180 minutes; and ST method used temperature of 120, 140, 160, 170 and 180 °C for 0, 5, 10 and 30 minute; while CSC method used temperature of 120, 140, 160, 180 and 200 °C for 0, 10, 20, 30 and 40 minutes. The results showed that the temperature and compression time contributed to the RS and WL value for all methods. Increasing compression temperature and time leads to decreased the RS value and to increased the WL value. The lower RS value indicated that S-OPT fixation would be better or high dimensional stability. Fixation of S-OPT by ST method was achieved at temperature of 170 °C for 30 min, CSC at temperature of 180 °C for 30 min, while HT method has not fixated until 200 °C for 180 min.

Pressure-Induced Densification of Oxide Glasses at the Glass Transition

Densification of oxide glasses at the glass transition offers a novel route to develop bulk glasses with tailored properties for emerging applications. Such densification can be achieved in the technologically relevant pressure regime of up to ~ 1GPa. However, the present understanding of the composition–structure–property relationships governing these glasses is limited, with key questions, e.g., related to densification mechanism, remaining largely unanswered. Recent advances in structural characterization tools and high-pressure apparatuses have prompted new research efforts. Here, we review this recent progress and the insights gained in the understanding of the influence of isostatic compression at elevated temperature (so-called hot compression) on the composition–structure–property relationships of oxide glasses. We focus on compression at temperatures at or around the glass transition temperature (Tg), with relevant comparisons made to glasses prepared by pressure quenching and cold compression. We show that permanent densification at 1 GPa sets-in at temperatures above 0.7Tg and the degree of densification increases with increasing compression temperature and time, until attaining an approximately constant value for temperatures above Tg. For glasses compressed at the same temperature/pressure conditions, we demonstrate direct relations between the degree of volume densification and the pressure-induced change in micro-mechanical properties such as hardness, elastic moduli, and extent of the indentation size effect across a variety of glass families. Furthermore, we summarize the results on relaxation behavior of hot compressed glasses. All the pressure-induced changes in the structure and properties exhibit strong composition dependence. The experimental results highlight new opportunities for future investigation and identify research challenges that need to be overcome to advance the field.

Quality Improvement of Oil Palm Trunk Properties by Close System Compression Method

ABSTRACT Densification of the inner part of oil palm trunk (OPT) by the close system compression (CSC) method was performed in this study. The effects of the compression temperature and time on the anatomical, physical and mechanical properties of OPT were evaluated. The inner part of OPT with an initial average density of 0.3 g/cm 3 was used as samples. Oven-dried samples were immersed in water and vacuumed until fully saturated andthen compressed by CSC at 120, 140, 160 or 180℃ for 10, 20, 30 or 40 min. The anatomical characteristics of transverse and radial sections before and after compression were compared by optical microscopy. The phys-ical and mechanical properties, including the density, recovery of set (RS), modulus of elasticity (MOE), mod-ulus of rupture (MOR), and compression parallel to grain were examined. It was observed that the anatomical characteristic of the inner part of OPT (i.e., vascular bundles, vessels, and parenchyma tissue) became flattened,fractured, and collapsed after compression by CSC. The RS decreased with increasing compression temperatureand time. The lower RS indicated high dimensional stability. The physical and mechanical properties (i.e., den-sity, MOR, MOE, and compressive strength) of the inner part of OPT increased with increasing compression temperature and time. Compression by the CSC method at 160℃ for 40 min was the optimum treatment. Keywords : close system compression, compressed wood, oil palm trunk, physical and mechanical properties, recovery of set

Ferrite grain refinement in low carbon Cu–P–Cr–Ni–Mo weathering steel at various temperatures in the (α + γ) region

Self-designed Cu–P–Cr–Ni–Mo weathering steel was subjected to compression test to determine the mechanism of ferrite grain refinement from 750°C to 925°C. Optical microscopic images showed that ferrite grain size declined, whereas the ferrite volume fraction increased with increasing compression temperature. Electron backscatter diffraction patterns revealed that several low-angle boundaries shifted to high-angle boundaries, thereby generating fine ferrite grains surrounded by high-angle boundaries. Numerous low-angle boundaries were observed within ferrite grains at 750°C, which indicated the existence of pre-eutectoid ferrite. Results showed that ferrite grain refinement could be due to continuous dynamic recrystallization at 750°C and 775°C, and deformation-induced ferrite transformation could be the main mechanism at 800°C and 850°C. Fine equiaxed ferrite grains with size ranging from 1.77μm to 2.69μm were produced in the (α+γ) dual-phase region.

Contributions of microstructural features to the integrated hardness of TA15 titanium alloy

Analysis of the contributions of microstructural features to integrated property of TA15 titanium alloy is a crucial issue for microstructure design and obtaining desired material properties. To this end, various microstructural features, such as equiaxed primary α phase (αp) and its boundary (αGB), transformed β matrix (βt) consisting of α plate and residual β phase (βbase) as well as the interface between them (βGB) were obtained by different isothermal compression and heat treatment conditions. Nanoindentation and Vickers hardness tests were then performed on these features to investigate their contributions to the integrated property. It is found that the hardness of αp varies slightly with the compression and heat treatment temperatures. The hardness of βt decreases while the hardness of integrated microstructure increases with increasing compression temperature. Moreover, the hardness values of βt and integrated microstructure are larger when the heat treatment temperatures are higher. By considering the hardness and volume fraction of each microstructural feature, it is also found that the contributions of microstructural features to the integrated hardness increase in the order of αGB, αp, βGB, βbase. The contributions of αp and αGB decrease while those of βbase and βGB increase with increasing compression temperature. In addition, the contributions of βbase and βGB to the integrated hardness can be further adjusted by heat treatment under different temperatures.

Behavior of Flow Stress of Al-Mn Alloy during Hot Compression

The behavior of flow stress of Al-Mn alloy during hot compression at the condition of ε=0.05,0.5,5,25s-1 while the temperature range from 300°C to 450°C was studied by Gleblee-3500. The results show that the Al-Mn alloy possess the remarkable characteristic of a peak stress, followed by a steady-state flow stress when deformed in the temperature range from 300°C to 450°C with a strain rates range from 0.05s-1 to 0.5s-1.When the strain rate is higher than 5s-1 dynamic recrystallization will happen. The true stress decrease with increasing compression temperature and increases with the increasing strain rate. A constitution equation which can describe the relationship of ε,T and σ is achieved. Also the activation energy for deformation is calculated.

열압밀화 라디에타 소나무재의 역학적 특성

본 연구에서는 압체온도와 시간에 따른 열압밀화 라디에타 소나무재의 역학적 특성을 조사하였다. 종압축강도와 휨강도는 압체온도와 시간의 증가와 함께 증가하였다. 그러나 압체온도 <TEX>$220^{\circ}C$</TEX>에서는 열화로 인해 오히려 감소된 값을 나타내었다. 표면경도는 압체온도의 증가와 함께 증가하였으며, 압체시간이 표면경도에 미치는 영향은 미약하였다. 못뽑기저항의 경우 접선단면의 저항력이 가장 높았으며, 압체온도와 시간에 의한 영향은 거의 나타나지 않았다. The mechanical properties of heat-compressed Radiata pine (Pinus radiata D.Don) by compression temperature and time were investigated. The compressive strength and bending strength of heat-compressed wood increased with increasing compression temperature and time. But the compressive strength and bending strength decreased with press temperature <TEX>$220^{\circ}C$</TEX>. It was considered due to thermal degradation during high temperature conditions. The surface hardness of heat-compressed wood increased with increasing compression temperature. However, the effect of compression time was negligible. The nail holding power was not affected by compression temperature and time.

라디에타소나무 열압밀화 목재의 경도와 치수안정성 - 압체 온도와 시간의 영향 -

라디에타 소나무(Pinus radiata D.Don)를 이용하여 압체 온도와 시간에 따른 압밀화 목재의 경도와 치수안 정성을 조사하였다. 압체 온도가 상승함에 따라 표면경도도 함께 증가하였다. 열압체 시간 30분을 기준으로 압체 온도 <TEX>$70^{\circ}C$</TEX>에서는 경도 값이 5.0 N/<TEX>$mm^2$</TEX>, <TEX>$220^{\circ}C$</TEX>에서 15.6 N/<TEX>$mm^2$</TEX>으로 312% 향상되었으며, 60분에서는 313%, 90분에서는 224% 향상되는 것으로 나타났다. 치수회복실험 결과 열압체 온도가 상승함에 따라 치수고정효과는 상승한 반면 압체 시간의 증가에 의한 치수고정효과는 미약하였다. 접촉각 측정결과 압체 온도와 시간의 증가와 함께 접촉각도 증가했으며 압체 온도 <TEX>$220^{\circ}C$</TEX>에서는 <TEX>$90^{\circ}$</TEX> 이상의 접촉각을 나타내어 표면이 소수성을 나타냄을 알 수 있었다. It was investigated the hardness and dimensional stability of heat-compressed wood by compression temperature and time. The surface hardness of heat-compressed wood increased with increasing compression temperature. The lowest hardness value (5.0 N/<TEX>$mm^2$</TEX>) was observed in the temperature <TEX>$70^{\circ}C$</TEX> while the highest value (15.6 N/<TEX>$mm^2$</TEX>) was obtained in compression temperature <TEX>$220^{\circ}C$</TEX>. Dimensional recovery test results showed that fixation of compression set improved with increasing compression temperature. However, the fixation effects were negligible by press time. Contact angle increased with increasing press temperature and time.

Effect of Mg 17Al 12 precipitates on the microstructural changes and mechanical properties of hot compressed AZ91 magnesium alloy

During hot compression, Mg 17Al 12 (β) precipitates show strong influence on the microstructural changes of 415 °C-24 h homogenized AZ91 alloy. When compressed at 300 °C and 350 °C, dynamic recrystallization (DRX) only occurs near grain boundaries with discontinuous β precipitate pinning at the newly DRXed grain boundaries. With increasing compression temperature and decreasing strain rate, the β-precipitating region expands; however, the amount of pinning precipitates decreases, resulting in increases in the DRX ratio and average DRXed grain size. With a compression ratio of only 50%, the specimen compressed at 350 °C and a strain rate of 0.2 s −1 (designated 350 °C-0.2 s −1 compressed specimen) shows an ultimate tensile strength (UTS) of 334 MPa, a 0.2% proof stress (PS) of 195 MPa and an enough elongation of 17.9%. After a subsequent aging treatment at 180 °C, due to the large number of β precipitates, the strength of the compressed specimens are further improved, and the specimen peak aged after compression at 400 °C and 0.2 s −1 shows UTS of 364 MPa and PS of 248 MPa with a moderate elongation of 7.7%.

Effect of Strain Rate on the High-Temperature Deformation Behavior of Nb&lt;SUB&gt;3&lt;/SUB&gt;Al Hipped from Prealloyed Powder

The effect of strain rate on stress-strain curves and deformation microstructures of Nb 3 Al at high temperatures was examined. Specimens prepared by hot isostatically pressing (HIP) Nb-Al alloy powder under 200 mesh size contain Nb 3 Al over 90% in volume. The concentration of aluminum in Nb 3 Al, measured by an electron probe micro analyzer (EPMA), is determined to be 23.4 mol%. Compression tests were carried out above 1273 K at four initial strain rates, 1.68 x 10 -2 s -1 , 1.67 x 10 -3 s -1 , 1.67 x 10 -4 s -1 and 3.34 x 10 -5 s -1 . Yield stress increases with increasing the initial strain rate and with decreasing compression temperature. In this experiment, stress-strain curves except for samples compressed at the initial strain rate of 3.34 x 10 -5 s -1 at 1673 K and 1773 K, and 1.67 x 10 -4 s -1 at 1773 K show a distinct peak stress followed by deformation softening. This peak stress is regarded to be caused by dynamic recrystallization, because the samples compressed at 1473 K show the typical necklace structure. Nb 3 Al can deform plastically to a large strain by dynamic recrystallization accompanied by grain boundary sliding. The dynamically recrystallized grain size increases and the peak stress on stress strain curves becomes indistinct with decreasing the initial strain rate and with increasing compression temperature.

The isothermal compression response of a near γ-TiAl + W intermetallic

Hot isostatically pressed Ti-48%Al-2%W powder compacts were isothermally compressed between 900 °C and 1200 °C, and at constant strain rate in the range 10 −1 to 10 −4 s −1. The deformation processes occurring are determined by correlation of the stress-strain response, strain rate sensitivity exponent m and activation energy, with the deformed microstructures. The resulting “deformation map” indicates that at low temperatures and high strain rates, mechanical twinning and dislocation generation cause a high flow stress, low m and high activation energy. Increasing compression temperature causes dynamic recrystallization, flow softening and increased m. Concurrent dynamic recrystallization and superplasticity can occur, with m as high as 0.44. At high temperatures and strain rates <10 −3 s −1, superplastic deformation is accompanied by grain coarsening. A “forging map” indicates that cracking after 120% engineering strain can be avoided if appropriate compression parameters are applied.