Densification Kinetics of Steel Powders during Direct Laser Sintering

Simchi Abdolreza,Petzoldt Frank 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

It is known that powder characteristics including particle size and distribution, particle shape, and chemical composition are important parameters which influence direct laser sintering of metal powders. In this paper, we introduce a first order kinetics model for densification of steel powders during laser sintering. A densification coefficient (K) is defined which express the potential of different powders to be laser-sintered to a high density dependent on their particle characteristics.

Processing of Tin Oxide Nanoparticles by Inert Gas Condensation Method and Characterization

Simchi Abdolreza,Kohi Payam 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

Tin oxide nanoparticles (n-SnO and ) were synthesized by the inert gas condensation (IGC) method under dynamic gas flow of oxygen and argon at various conditions. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) method were used to analysis the size, shape and crystal structure of the produced powders. The synthesized particles were mostly amorphous and their size increased with increasing the partial pressure of oxygen in the processing chamber. The particles also became broader in size when higher oxygen pressures were applied. Low temperature annealing at in air resulted to crystallization of the amorphous n-SnO particles to .

Co-sintering of M2/316L Layers for Fabrication of Graded Composite Structures

Firouzdor V.,Simchi A.,Kokabi A.H. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

This paper presents the densification and microstructure evolution of bilayer components made from 316L stainless steel and M2 High speed steel during co-sintering process. The sintering was carried out at temperatures ranging from in a reducing atmosphere. The addition of boron to 316L was examined in order to increase the densification rate and improve the sintering compatibility between the two layers. It was shown that the mismatch strain bettwen the two layers induces biaxial stresses during sintering, influencing the densification rate. The effect of boron addition was also found to be positive as it improves the bonding between the two layers.

Investigation on the Sintering Behavior of P/M Al-Zn-Mg-Cu Alloy

Shahmohammadi M.,Simchi A.,Danninger H.,Arvand A. 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

In the present work, the sintering behavior of high strength Al-5.6Zn-2.5Mg-1.6Cu (in wt.%) alloy compacts prepared from elemental powders was investigated. Microstructural evaluation was accompanied by XRD and DSC methods in order to determine the temperature and chemical composition of the liquid phases formed during sintering. It was found that three transient liquid phases are formed at 420, 439 and 450 . Microstructural study revealed the progressive formation of sintered contacts due to the presence of the liquid phases, although the green compact expands as a result of the melt penetration along the grain boundaries. While Zn melts at , the intermetallic phases formed between Al and Mg were found to be responsible for the formation of liquid phase and the dimensional change at higher temperatures.

Hot Deformation Behavior of P/M Al6061-20% SiC Composite

Asgharzadeh Hamed,Simchi Abdolreza 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

In the present work, hot workability of particulate-reinforced Al6061-20%SiC composite produced by direct hot extrusion technique was studied. Uniaxial hot compression test at various temperatures and strain rates was used and the workability behavior was evaluated from the flow curves and the attendant microstructures. It was shown that the presence of SiC particles in the soft Al6061 matrix deteriorates the hot workability. Bulging of the specimens and flow lines were observed, which indicate the plastic instability during hot working. Microstructure of the composites after hot deformation was found to be heterogeneous, i.e. the reinforcement clusters were observed at the flow lines. The mechanism of deformation was found to be controlled primarily by dynamic recrystallization.

Dynamic restoration and microstructural evolution during hot deformation of a P/M Al6063 alloy

Asgharzadeh, H.,Simchi, A.,Kim, H.S. Elsevier 2012 Materials science & engineering. properties, micro Vol.542 No.-

<P><B>Highlights</B></P><P>► Restoration mechanisms in a P/M Al6063 alloy were studied. ► Microstrucural changes during hot deformation were analyzed by TEM and EBSD. ► The activation energy of the hot deformation was determined. ► Correlations between Zener–Hollomon parameters and the size of subgrains and recrystallized grains were established. ► DRV prevailingly occurred at high <I>Z</I> values DRX was the dominant mechanism at the low <I>Z</I> values.</P> <P><B>Abstract</B></P><P>Hot deformation behavior of Al6063 alloy produced by direct powder extrusion was studied by means of uniaxial compression test in the temperature range between 300 and 450°C and strain rate range between 0.01 and 1s<SUP>−1</SUP>. Electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM) were utilized to study the microstructure of the material before and after the hot deformation. The microstructure of the extruded alloy consisted of elongated grains within a subgrain structure and small grains free of low angle grain boundaries (LAGBs). An equiaxed duplex microstructure consisting of large substructured grains and fine grains separated by high angle grain boundaries (HAGBs) were observed after hot deformation. Evaluation of the hot-deformation activation energy using a hyperbolic sine law yielded a value of 198kJmol<SUP>−1</SUP>. The kinetic analysis and microstructural changes suggest that dynamic restoration mechanisms, i.e., dynamic recovery (DRV) and dynamic recrystallization (DRX), are operative to cause flow softening during hot compression. Correlations between Zener–Hollomon parameters and the size of subgrains and recrystallized grains were established. It was found that DRV prevailingly occurred at high <I>Z</I> values (<I>Z</I>>1.12×10<SUP>16</SUP>) while DRX was the dominant mechanism at the low <I>Z</I> values.</P>

Nanoporous composites of activated carbon-metal organic frameworks for organic dye adsorption: Synthesis, adsorption mechanism and kinetics studies

Mahdi Hasanzadeh,Abdolreza Simchi,Hossein Shahriyari Far 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.81 No.-

Activated carbon (AC) is an inert adsorbent material that has widely been used in water treatment orremoving of environmental pollutants from water. In order to improve the adsorption of AC, which highlydepends on its pore size and surface area, we prepared highly porous adsorbent composites of activatedcarbon (AC)/chromium-based MOF (MIL-101(Cr)). The composite has a high specific surface area of2440 m2 g 1 and total pore volume of 1.27 cm3 g 1. To show the efficiency of the composite as anadsorbent, the removal kinetics of anionic dyes (Direct Red 31 and Acid Blue 92) from aqueous solutionsdependent on the amount of composite, adsorption time, concentration of dye and pH is demonstrated. Itis shown that the kinetics of organic dye removal by AC@MIL-101(Cr) composite is faster than MIL-101(Cr) under near neutral pH conditions. The half-time of removal is about 3 min while about 85% of the dyeis removed after 5 min. This study provides new idea into the design and synthesis of highly efficientnanoporous adsorbent based on MOFs for removal of pollutants as well as organic dyes from wastewater.

3D Printing of Biocompatible PM-materials

Dourandish Mahdi,Godlinski Dirk,Simchi Abdolreza 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

The fabrication of complex-shaped parts out of Co-Cr-Mo alloy and 316L stainless steel by three-dimensional printing (3DP) was studied using two grades of each alloy with average particle size of 20 and , respectively. To produce sound specimens, the proper 3DP processing parameters were determined. The sintering behavior of the powders was characterized by dilatometric analysis and by batch sintering in argon atmosphere at for 2h. The 3DP process has successfully produced complex-shaped biomedical parts with total porosity of 12-25% and homogenous pore structure, which could be suitable for tissue growth into the pores.

Creep Behavior of Hot Extruded Al-5% SiC Composite Powder

Monnazah A. Hosseini,Simchi A.,Reihani S.M. Seyed 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1

The creep behavior of Al-5vol.% SiC composite was investigated. The composite powder was produced by mechanical milling and hot extruded at at ratio of 16:1. A creep test was carried out at a constant load at 598, 648, and 673 K. Using the steady-state equations, the threshold stress and the stress exponent of the creep as a function of temperature were determined. The stress exponent was found to be 3 at the temperature of 673 K and 8 at 598 and 648 K. The dependency of the threshold stress to temperature obeys the Arrhenius relationship with the energy term of .

Role of Grain Size and Oxide Dispersion Nanoparticles on the Hot Deformation Behavior of AA6063: Experimental and Artificial Neural Network Modeling Investigations

A. Asgharzadeh,H. Asgharzadeh,A. Simchi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

The hot deformation behavior of coarse-grained (CG), ultrafine-grained (UFG), and oxide dispersion-strengthened (ODS)AA6063 is experimentally recognized though carrying out compression tests at different temperatures (300–450 °C) andstrain rates (0.01–1 s−1). Microstructural studies conducted by TEM and EBSD indicate that dynamic softening mechanismsincluding dynamic recovery and dynamic recrystallization become operative in all the investigated materials depending on theregime of deformation. Moreover, the high temperature flow behavior is considerably influenced by the initial grain structureand the presence of reinforcement particles. The constitutive and artificial neural network (ANN) models were used to studythe high-temperature flow behavior of the investigated alloys. To establish an accurate ANN model, material characteristicsalong with the processing parameters are deliberated. An Arrhenius type constitutive model with a strain-compensation termis employed to predict the flow stress of AA6063 alloys. The relative error associated with the constitutive and ANN modelsin the prediction of the flow stress is obtained 9.56% and 2.02%, respectively. The analysis indicates that the developed ANNmodel is more accurate in the prediction of flow stress with at least 78% less error in comparison to the constitutive model.