Hot Densification Research Articles

Research on the hot densification mechanism of biomass wastes based on molecular dynamics simulation and components adjustment method

The hot densification process can be used to prepare the biofuel pellets and diversified densification materials with suitable mechanical strength to overcome the natural defects of low energy density and loose structure of biomass wastes and achieve the high value utilization of the renewable resources. In this study, the two typical biomass wastes, cotton stalk (CS) and Chinese fir wood sawdust (WS) are used for the hot densification investigation (85 °C), and the microscopic evolution behavior of the biomass components during the hot densification process is explored through the combination of the component adjustment method and molecular dynamics simulation. The results show that cellulose is the key component to the mechanical strength of biomass pellet, which plays the crucial role of skeleton support in the densification process, and the strength of pellet is positively correlated with the increasing addition ratio of cellulose. Furthermore, crystalline cellulose exhibits the strongest bonding properties in the hot densification process due to the formation of rich hydrogen bonds and the increasing intermolecular attraction force. Lignin has the poorest capability for hydrogen bond formation, and its addition increases the van der Waals repulsive forces, resulting in the poorest densification performance. Hemicellulose shows the better adhesion capability than lignin due to its glassy transition (83.34 °C) and the suitable addition can greatly improve the mechanical property of the pellet, up to 14.26 MPa. There exists the strongest synergistic effect between cellulose and hemicellulose, which is beneficial to the bonding performance between particles to different extent. Hot densification process can promote the formation of hydrogen bond connections between molecules/atoms and the increase of the van der Waals repulsive force in the further compression. The densification performance of biomass is the combined effect of the physical forces, including electrostatic force and van der Waals force.

Features of the Plastic Flow of Sintered Al–12Si–xSn Alloys

The feasibility of obtaining a self-lubricating composite material of the Al–Sn system with the alloyed matrix by the liquid-phase sintering of compacts obtained from the mixture of powders of the eutectic Al–12Si alloy and tin powders was investigated. The porosity of the raw compacts was ~10%; the strength of the sintered Al–12Si–xSn composites was significantly lower as compared with the additive value. The porosity of compacts decreased and the strength reached the theoretical value after additional hot densification of the sintered samples at 200 and 250°C (lower and higher than the tin melting point). The plasticity of composites under compression after densification increased as well and showed its maximum in the composite with 10–20% Sn. Analysis of the compression curves showed that, for the sintered composites, the long linear stage of plastic flow with a low coefficient of strain hardening is a characteristic feature. With the increase in the tin content, the stage of the linear flow shortens and with the 40% Sn concentration disappears. The transcrystalline localized flow and material cracking is observed before fracture.

Impact of the Structure on Mechanical and Tribological Properties of Sintered (Al–12 Si)–40 Sn Alloy

Interaction of the structure of the composite alloy (Al–12 Si)–40 Sn with its mechanical and tribological properties was studied. The alloy was obtained by the liquid-phase sintering of powder briquettes made of the powder mix of tin PO-2 and an atomized aluminum alloy of the eutectic composition Al–12 Si. Sintering was carried out at a temperature below the melting point of the eutectic; otherwise, the sample melted and lost its shape. It was found that the given sintering temperature does not make it possible to obtain samples with high density; their residual porosity was 6–8% and it almost was not decreased with the increase in the sintering time. The obtained material had low mechanical properties, which slightly improved with the increase in the sintering time to two hours. At the same time, the amount of exuded and evaporated tin noticeably increased. Taking into account the undesirable phenomena that occurred during a long exposure of sintered samples at high temperature, the hot densification was carried out after the short-term sintering. Densification of the sintered samples aiming at removal of the residual porosity was carried out in a closed mold under pressure above the ultimate strength of the alloy. It was established that such operation contributed both to significant improvement of strength and ductility of the studied material. In addition, the obtained nonporous material had high wear resistance under dry friction against a steel counterbody; it was especially noticeable during friction under high pressure. The wear rate of samples with a matrix made of the aluminum-silicon alloy was 30% lower as compared with the alloy with the matrix made of pure aluminum at all other conditions being equal.

Superior transport Jc obtained in in-situ MgB2 wires by tailoring the starting materials and using a combined cold high pressure densification and hot isostatic pressure treatment

The best Jc performance (8×104A·cm−2 at 10T, 4.2K) has been obtained in our work among all the in-situ powder-in-tube (PIT) MgB2 wires reported so far by tailoring their boron and magnesium precursors, as well as employing appropriate high pressure during the manufacturing process. Moreover, the second stage densification using the special HIP has been applied to commercial long-length wire. Our work suggests that the economical starting precursors and the combination of cold and hot densification techniques could represent a promising alternative for industrial and economical production of practical MgB2 wires with excellent Jc.

Flow and Densification Behaviors of Sintered P/F-10C50 Steel under Hot Compression

The hot deformation and densification behaviors of sintered P/F-10C50 steel were investigated by hot compression tests on Gleeble-1500 thermal mechanical simulator at the temperature ranging from 900 °C to 1000 °C and the strain rate ranging from 0.1 s-1 to 10 s-1. The flow and densification characteristics of the tested specimens at different deformation temperatures and strain rates were studied. The flow stress of the sintered steel persistently increases until the end of the test as the result of matrix and geometric work hardening. The higher deformation temperature and strain rate are conductive to the healing of the pores and promote the densification of the sintered steel, while the higher deformation temperature and lower strain rate impede the densification. The constitutive equation of the sintered steel is established by the means of stepwise regression. The flow stresses predicted by the established constitutive equation are in good agreement with the experimental values, and the correlation coefficient (R) and the average absolute relative error (AARE) are 0.9931 and 3.52%, respectively. These results demonstrate the hot deformation behaviors of the sintered P/F-10C50 steel are excellently predicted by the established constitutive equation.

Modeling Aspects of Hot Densification and Deformation Studies on Al–TiB2 Composite Preforms

The modeling aspects of hot deformation and densification behavior of Al–TiB2 composites are discussed in the present paper. A constitutive relation capable of relating the flow stress to the strain at different temperatures, namely 200°C, 300°C, 400°C, and 500°C, and at different strain rates, namely 0.12, 0.14, 0.16, and 0.18 s−1, have been developed and the developed relation has been used to predict the deformation behavior and the densification attained for different deformation levels and temperatures. The distribution of density and the location of maximum and minimum density zones have been predicted using DEFORM 2D, a finite element analysis (FEA) based software. The damage mechanism that governs the densification process has been identified and the critical damage value has been found.

Design and Verification of the Parameters of Hot Forging of Ti10V2Fe3Al Alloy Compacts

This research work was focused on the application of powder metallurgy technology to the production of high-quality products from Ti10V2Fe3Al alloy. For the purpose of investigations hot compaction and hot closed-die forging processes were used. As an initial material a mixture of elemental powders was applied. As a result of hot densification, fully densified semi-products were obtained (99.4 % relative density). Numerical modelling of forging of a selected forging was performed using finite element method. Various options of forging process conditions were applied. The designed parameters of forging technology were verified by means of trials performed in industrial conditions. The quality of the product was estimated by microstructure observations. It was found that hot forging of compacted mixture of elemental powders resulted in obtaining defect-free gear wheel showing the relative density of 99.8 ±0.2 %.

Application of rapid solidification powder metallurgy processing to prepare Cu–Al–Ni high temperature shape memory alloy strips with high strength and high ductility

Cu–Al–Ni high temperature shape memory alloy (HTSMA) strips were successfully prepared from rapid solidified water atomized Cu–Al–Ni pre-alloyed powders via hot densification rolling of unsheathed sintered powder preforms. Finished heat-treated Cu–Al–Ni alloy strips had fine-grained structure, average grain size approximately 16μm, and exhibited a combination of high strength and high ductility. It has been demonstrated that the redistribution of nano-sized alumina particles, present on the surface as well as inside the starting water atomized Cu–Al–Ni pre-alloyed powder particles, due to plastic deformation of starting powder particles during hot densification rolling resulted in the fine grained microstructure in the finished SMA strips. The finished SMA strips were almost fully martensitic in nature, consisting of a mixture of β1′ and γ1′ martensite. The average fracture strength and fracture strain of the finished SMA strips were 810MPa and 12%, respectively, and the fractured specimens exhibited primarily micro-void coalescence type ductile nature of fracture. Finished Cu–Al–Ni SMA strips exhibited high characteristic transformation temperatures and an almost 100% one-way shape recovery was obtained in the specimens up to 4% applied deformation pre-strain. The retained two-way shape memory recovery increased with increasing applied training pre-strain, achieving a maximum value of 16.25% at 5% applied training pre-strain.

The influence of densification temperature and the size of powder particles on the properties of isotropic Nd-Fe-B magnets made of quenched ribbons

The influence of densification temperature and the size of powder particles on magnetization of remanence Jr, coercivity JHc of hot-densified Nd-Fe-B magnets made of MQP-A quenched ribbons was investigated. A connection between magnetic properties, parameters of production process and microstructure of the magnet was confirmed. It was found that the remanence of isotropic magnet depends on temperature of hot densification process but is practically independent of the size of powder particles. On the other hand, the temperature of hot densification process and the size of powder particles have a substantial influence on coercivity.

Hot Dynamic Densification of Materials by Utilizing Underwater Shock Wave

Hot dynamic densification method was developed by combining self-propagating high temperature synthesis (SHS) with explosively shock powder compaction technique. This method is extremely short time processing. The main purpose in this study is to perform from synthesis to densification of TiB2-TiN system high temperature ceramic composites and TiB2-TiNi-Cu system functionally graded materials (FGMs) in one step. In TiN-TiB2 ceramic composites, they showed up to 95% of relative density. It was appeared by TEM observations that both the two phases joined tightly each other. The FGMs also were produced by the same technique. They indicated no interlayer exfoliation and no macro cracks after thermal shock tests from 973 K to room temperature. It was shown that thermoelastic property of intermetallic TiNi phase as intermediate layer between ceramics and metal layers operated effectively.

Synthesis and properties of Cu–Al–Ni shape memory alloy strips prepared via hot densification rolling of powder preforms

Cu–Al–Ni shape memory alloy strips were successfully prepared by a powder metallurgy route consisting of preparing powder preforms from premixed Cu, Al and Ni powders by cold compaction, stepwise sintering in the range 873–1273 K, followed by unsheathed multipass hot rolling at 1273 K in protective atmosphere. The densification behaviour of the sintered powder preforms during hot rolling has been discussed. Homogenisation of the hot rolled strips was carried out at 1173 K for 4 h. It has been shown that the finished Cu–Al–Ni alloy strip consisted of self-accommodated plates ofβ' and γ' martensites together with a small amount of nanocrystalline Cu9Al4 phase. The finished hot rolled Cu–Al–Ni strips had fracture strength of 476 MPa, coupled with 2·5% elongation. The shape memory tests showed almost 100% recovery after 10 thermomechanical cycles in the hot rolled strips at 1 and 2% applied prestrain.

Microstructure and properties of Cu–Al–Ni shape memory alloy strips prepared via hot densification rolling of argon atomized powder preforms

Abstract In the present work, Cu–Al–Ni SMA strips with grain size less than 100 μm were successfully prepared via a novel powder metallurgy route involving hot densification rolling of unsheathed sintered powder preforms prepared from argon atomized pre-alloyed Cu–Al–Ni powder. It has been shown that the hot rolled Cu–Al–Ni strips exhibited a very small grain growth during heat treatment at 950 °C up to 4 h. This behavior was attributed to the pinning effect of nano-sized alumina segregated on the grain boundaries. It was established that the grain size of the finished Cu–Al–Ni strips is governed by the starting powder particle size, and the mechanism of this aspect has been discussed. The finished heat-treated Cu–Al–Ni alloy strips consisted of elongated shape grains, with average grain size approximately 27 μm. The heat treated strips were fully martensitic in nature consisting of self-accommodated β ′ 1 martensite along with small amount of γ ′ 1 martensite. The heat treated strips had an extremely good combination of average fracture strength (∼626 MPa) and fracture strain (∼13.5%). The two-way shape memory strain was found approximately 0.23% after 25 training cycles at 4% applied training strain.

Processing and Characterization of Cu-Al-Ni Shape Memory Alloy Strips Prepared from Prealloyed Powder by Hot Densification Rolling of Powder Preforms

The present work deals with the preparation of near-full density Cu-Al-Ni shape memory alloy (SMA) strips from argon-atomized prealloyed powder via a powder metallurgy (PM) route comprising cold die compaction to prepare powder preforms, sintering, and hot densification rolling of unsheathed sintered powder preforms under protective atmosphere at 1273 K (1000 °C). It has been shown that argon-atomized spherical Cu-Al-Ni SMA powder consisted of very fine equiaxed grains and no appreciable grain growth occurred during sintering at 1273 K (1000 °C). It also has been shown that no appreciable densification occurred during sintering, and densification was primarily achieved by hot rolling. The densification behavior of the sintered powder preforms during hot rolling was discussed. The hot-rolled Cu-Al-Ni strips were heat-treated at 1223 K (950 °C) for 60 minutes and water quenched. The heat-treated strips consisted of equiaxed grains with average size approximately 90 μm. The heat-treated Cu-Al-Ni SMA strips consisted of self-accommodated \( \beta_{1}^{'} \) martensite primarily, and showed smooth \( \beta_{1} \Rightarrow \beta_{1}^{'} \) transformation behavior coupled with a very low hysteresis (≈25 K (25 °C)). The heat-treated strips exhibited an extremely good combination of mechanical properties with fracture strength of 530 MPa and 12.3 pct fracture strain. The mode of fracture in the finished strip was primarily void-coalescence-type ductile together with some brittle transgranular type. The shape memory tests showed almost 100 pct one-way shape recovery after 100 bending-unconstrained heating cycles at 4 pct applied prestrain, exhibiting good stability of Cu-Al-Ni strips under thermomechanical actuation cycling. The two-way shape memory strain was found approximately 0.45 pct after 15 training cycles at 4 pct training strain.

Effects of cold and hot densification on the mechanical properties of a 7XXX series powder metallurgy alloy

The objective of this work was to investigate the effects of hot and cold swaging on the density and mechanical properties of a commercial Al–Zn–Mg–Cu powder metallurgy alloy known as Alumix 431D. To do so, as sintered samples of the PM alloy were swaged under a variety of conditions and characterised. For comparison purposes, equivalent characterisation tests were completed on the chemically similar wrought alloy 7075-T6. Cold swaging was moderately successful provided the as sintered billets were annealed or solutionised before densification. Here, modest improvements in density and tensile properties were noted. Hot swaging proved to be a more effective approach. Optimal properties were achieved when samples were preheated to 470 ± 10°C. When processed in this manner, a density of 99·6% of theoretical was realised while the tensile and fatigue properties exceeded those of the wrought 7075-T6 alloy tested for comparison purposes.

Deformation behaviors of porous 4032 Al alloy preform prepared by spray deposition during hot rolling

Rolling processing was selected to produce fully dense sheet from porous preform. Deformation behavior of the porous preform prepared by spray deposition during hot densification rolling has been investigated. The strain distribution in the deformation zone of the porous samples is analyzed. A notable deformation behavior is that the thickness reduction of the porous preform decreases from the surface to the center across the section, even though the total thickness reduction is up to 40% in a single pass, which is obviously different from the deformation characteristic of the fully dense metal. A decreased normal stress from surface to center and a lower work hardening effect during rolling of porous metal are supposed to be the main factors. When the longitudinal and transverse flow during rolling were retarded by contact friction, a decreased strain in length and width will result in a decreased thickness strain during rolling of fully dense metal due to a constant volume. However, the porous preforms tend to be compacted firstly near the surface of porous metal due to porosity.

Current and advanced hot densification processes : A. Bose. (Parmatech Corp, Petaluma, USA.)

The effect of ausforming on formation of upper bainite structure was investigated in Fe–9Ni–(0.15–0.5)C (mass%) alloys, focusing on the crystallographic feature of bainitic ferrite. The specimens were ausformed at 1073 or 873 K by 50% compressive reduction after austenitizing, and transformed at 623 K. Lath-shaped upper bainite structures similar to lath martensite are formed at 623 K. A bainite packet is partitioned into blocks of all the six variants of the K–S orientation relationship satisfying the same parallel close-packed plane relationship. In both of the non-ausformed and ausformed specimens, bainite blocks are coarsened with increasing carbon content. In the Fe–9Ni–0.15C alloy, the effect of ausforming on the bainite block width is small. For higher carbon alloys (Fe–9Ni–0.3C and 0.5C), bainite blocks are remarkably coarsened by the ausforming. In contrast, the ausforming refines lath martensite blocks in the Fe–9Ni–0.15C alloy but has a small effect in higher carbon alloys.

Changes in the longitudinal flow and apparent plastic poisson’s ratio of a porous metal strip during hot densification rolling

Analytical relationships between the longitudinal flow and the thickness deformation, and between the apparent plastic Poisson’s ratio and the relative density of a porous metal strip during hot rolling have been derived from geometrical considerations. Experimental data obtained from the hot rolling of porous copper strips of relative density of 0.4 have been shown to agree well with the results predicted from analytical relationships. Changes in the longitudinal flow and the apparent plastic Poisson’s ratio can be divided as taking place in three distinct stages of densification. Stage I,i.e., the densification up to the relative density of 0.70, involves the densification of the strip merely by decreasing the pore channel widths without closing them. Stage II,i.e., the densification from the relative density from 0.70 to that of 0.95, is associated with the patching of pore channels at some points, the number of which increases as the thickness deformation given to the strip increases. Stage III,i.e., the densification of the strip from the relative density of 0.95 and onward, involves the elimination of the newly formed closed porosity by shearing.

Properties of copper strip prepared from preformed cuprous oxide via concurrent reduction and sintering – hot densification rolling route

The properties of cold rolled and annealed copper strip obtained by hot rolling of cuprous oxide preform after concurrent reduction and sintering are described. It is shown that the copper strip has a tensile strength of 225 MN m−2 coupled with an elongation and electrical conductivity of respectively 47% and 98·4% IACS. The properties are similar to those of conventionally made electrolytic tough pitch copper and strips made by the conventional powder metallurgy route. The finished copper strip has a fine grain fully recrystallised structure and contains about 1·2 vol.-% of Cu2O inclusions having a mean size of about 1 μm in the rolling direction. The cold rolling and annealing behaviour of the copper strip is also briefly discussed.MST/687

Densification of porous powder preforms during hot forging. I. Processing lubricant for transverse hot forging

Use of lubricants 2, 3, 4 and 5 (Table 1) in transverse hot densification does not prevent buildup formation on the tool. By contrast, the specially developed molybdenum disulfide and graphite base lubricant 1 [13] exhibits excellent friction- and wear-reducing characteristics. With this lubricant it is possible to produce high-density P/M parts of considerable length by transverse hot forging without buildup formation on the tool and with little nonuniformity of deformation in the surface layers of the material.

Hot Impact Densification: A New Method for Producing High Density Ceramic Pellets with Close Shape Tolerances

Density and correct diameter of nuclear fuel pellets are usually achieved by sintering and subsequent circular grinding. Hot impact densification (HID) thermally squatted ceramic bodies can be directly high speed precision-molded in a cold die. For thermoshock-sensitive materials, a controlled cooling down procedure of some minutes is added. The feasibility of HID has been demonstrated on the laboratory scale on UO/sub 2/, UC, and some more materials at temperatures between 1700 and 2300/sup 0/C, pressures up to 800 N/mm/sup 2/. Shape tolerances are close, density can be exactly reproduced within a wide range. Tool wear seems to be no problem. Currently, a prototype facility for continuous performance is being developed.