Transient Liquid Phase Bonding of 17-4-PH Stainless Steel Using Conventional and Two-Step Heating Process

Mohammad J. Moradi,Esmaeil Emadoddin,Hamid Omidvar 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

Conventional and two-step heating transient liquid phase bonding (TLP) experiments of martensitic precipitation hardeningstainless steel 17-4-PH were studied employing AMS 4777 braze filler at temperature of 1050 °C for different times (15 to90 min) to accomplish the ideal brazing condition. The effect of TLP methods and bonding conditions on the microstructureand shear bond strength was investigated. The critical bonding time for isothermal solidification in conventional and two-stepheating TLP was 60 min and 45 min, respectively. The microstructure of isothermal solidification zone consisted of Ni-richsolid solution phase. Eutectic constituents Cr-rich boride and Ni3Siwere formed in the joint centerline in the athermallysolidified zone. In the conventional method planar interface was formed, however in TLP bonding under temperature gradientnon-planar interface was formed, high angel grain boundaries merged at the end of isothermal solidification and homogenousbond was produced. Due to the decrease of athermally solidified zone the shear strength increased by increasing the holdingtime and when using the two-step heating process because of better metal to metal contact, the shear strength was higher. The optimum condition was a temperature gradient TLP in 60 min bonding time, which led to shear strength of 435 MPa.

Functionally-Graded Shape Memory Alloy by Diffusion Annealing of Palladium-Coated NiTi Plates

Fatemeh Khaleghi,Mohammad Tajally,Esmaeil Emadoddin,Maryam Mohri 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.5

Diffusion annealing of palladium-coated Ti-Ni plates was performed at temperatures ranging from 900 °C to1,000 °C, to accomplish a compositional gradient in Ti-rich, Ti-Ni shape memory alloys. The aim of this study wasto increase the transformation temperatures and transformation temperature intervals. Palladium diffusion profileswere measured by energy dispersive spectroscopy, and the corresponding approximate diffusion coefficients ofthe annealed specimens were calculated. The Gaussian solution of Fick’s second law for the one-dimensional latticediffusion of a tracer was used. The transformation behavior studies were performed by differential scanningcalorimetry. It was depicted that annealed specimens show longer transformation intervals compared to the barealloy. In addition, annealed specimens showed improved shape memory properties that were attributed to thelower amount of Ti2Ni precipitates in the diffusion layer. The shape memory behaviour of the samples wasdetected using micro-indentation at room temperature, followed by heating them above the austenite formationtemperature to calculate the shape recovery ratio.

Simple Shear Extrusion of Al/Al2O3 Composite Prepared by Stir Casting and Hot Forging

Majed Zabihi,Fathallah Qods,Esmaeil Emadoddin 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.1

In this study, aluminum/alumina composites with 3 and 5 vol% reinforcement particles were manufactured via stir castingand hot forging; they were severely deformed by the simple shear extrusion (SSE) technique. Three SSE dies with differentdistortion angles were utilized in this work. The SSE-ed samples with α = 22.5° were then fractured after one pass, whileSSE-ed samples with α = 8 and 10° were deformed up to thirteen passes, successfully. Microstructural evolution, porositypercentage and micro hardness parameters were investigated after each process. Shear punch test was then used to evaluatethe mechanical properties. Additionally, the applied force and stress/strain distributions were evaluated by the finite elementmethod (FEM) code via ABAQUS® simulation software in different passes. Moreover, the effect of the SSE process on thefracture behavior of the commercial Al and aluminum matrix composite was studied. The results showed that the effectivestrain was increased with increasing the number of SSE passes and distortion angles, while the applied force was decreasedwith increasing the number of passes. Microstructure, bonding quality, hardness and porosity percentage were also improvedby using forging and SSE processes. During the process, ultimate shear strength was enhanced with increasing the amountsof effective strain; also, shear elongation percentage was decreased. Further, SEM observations showed that the fracturemode in the SSE-ed commercial Al sample was a typical ductile one, whereas the fracture mode was nearly shear ductilewith more flat surfaces in the Al-5 vol% Al2O3specimens.

Investigation of direct extrusion channel effects on twist extrusion using experimental and finite element analysis

Nouri, Mehran,Mohammadian Semnani, Hamidreza,Emadoddin, Esmaeil,Seop Kim, Hyoung Elsevier 2018 MEASUREMENT -LONDON- Vol.127 No.-

<P><B>Abstract</B></P> <P>Twist extrusion (TE) is a relatively new severe plastic deformation technique in which radial deformation is heterogeneously distributed in the sample. In this research, in order to achieve favorable properties, a direct extrusion (DE) channel was embedded after the twist zone at the bottom of the TE die. The plastic deformation behavior of aluminum alloy 6063 (AA6063) was investigated in the TE process, with and without the DE channel. AA6063 successfully underwent TE under the conditions designed using the finite element analysis. According to the simulation results, a very heterogeneous distribution of the equivalent plastic strain (PEEQ) was observed in TE, while the TE+DE simulation exhibited more homogeneous PEEQ in the central and lateral regions. Microstructural evolution analysis using scanning electron microscope and Vickers microhardness evaluations showed that utilizing the DE channel increased the hardness and provided a more homogenous microstructure. Moreover, tensile testing results indicated an increase in strength and enhanced mechanical properties of the TE+DE processed AA6063.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Innovative twist extrusion was achieved by embedding a direct extrusion channel after the twist zone. </LI> <LI> Finite element analysis showed that the direct extrusion channel decreased sample deformation heterogeneity. </LI> <LI> All data indicated that absence of sufficient back pressure led to distortion and elongation of samples. </LI> <LI> The best microstructure was achieved by combining twist extrusion and direct extrusion channel. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Computational and Experimental Studies on the Effect Back Pressure on Twist Extrusion Process

Mehran Nouri,Hamidreza Mohammadian Semnani,Esmaeil Emadoddin 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8

In the current study, aluminium 6063 alloy (AA6063) was successfully gain refined by twist extrusion (TE) technique. TEis a representative severe plastic deformation process to fabricate ultrafine-grained in bulk materials by repetitive passes. In order to investigate the influence of back pressure, a direct extrusion (DE) channel was embedded after the twist zoneand the behavior of AA6063 was investigated and compared with and without this channel. Analyzing microstructuralevolutions by scanning electron microscope and Vickers microhardness evaluations showed that, adding the DE channelincreased the hardness distribution and a more homogenous structure was obtained. Finite element analysis was utilized tostudy the distribution of the equivalent plastic strain (PEEQ) numerically. According to the obtained results, with applyingthe TE process, strain increase was observed all over the sample surface, whereas modeling the DE channel after the twistzone caused a better homogeneity in the PEEQ distribution of the transverse cross-section. The PEEQ distribution duringTE process can be correlated to the extent of grain refinement and the uniformity of ultrafine grains. This method seems tobe very interesting and very promising for the future industrial application.