Showing 8 results for Niti
A. Poladi, M. Zandrahimi,
Volume 5, Issue 3 (9-2008)
Abstract
Abstract: Austenitic stainless steels exhibit a low hardness and weak tribological properties. The
wear behaviour of austenitic stainless steel AISI 316 was evaluated through the pin on disc
tribological method. For investigating the effect of wear on the changes in microstructure and
resistance to wear, optical microscopy and scanning electron microscope were used. The hardness
of the worn surfaces was measured with a micro-hardness tester. Worn surfaces were analyzed
through X-ray diffraction. Results showed that with increasing the sliding distance and applied
load, the austenite phase partially transformed to ά martensite, and there was no trace of ε phase
detected. Due to the formation of probably hard and strong martensite phase, as the sliding
distance and applied load increased, the hardness and the wear resistance of the material was
increased. Wear mechanism was on the base of delamination and abrasion.
H. Shahmir, M. Nili Ahmadabadi, F. Naghdi,
Volume 5, Issue 4 (12-2008)
Abstract
Abstract: In the present study the effect of thermomechanical treatment (cold work and annealing) on the
transformation behavior of NiTi shape memory alloys was studied. Differential scanning calorimetry was used to
determine transformation temperature and its relation to precipitates and defects. Three alloys including Ti-50.3at.%
Ni, Ti-50.5at.% Ni (reclamated orthodontic wires) and 50.6at.% Ni alloy were annealed at 673 K and 773 K for 30
and 60 min after 15% cold rolling. It was found that the transformation characteristics of these alloys are sensitive to
annealing treatment and composition. The temperature range of transformation is broadened during cold working and
after subsequent annealing, the intermediate phase was appeared. The peaks become sharper and close together on
each cooling and heating cycle with increasing annealing temperature and time
S. Noori, J. Khalil-Allafi,
Volume 12, Issue 2 (6-2015)
Abstract
The effect of anodic oxidation of a NiTi shape memory alloy in sulfuric acid electrolyte on its surface
characteristics was studied. Surface roughness was measured by roughness tester. Surface morphology was studied
using optical microscopy (OM) and scanning electron microscopy (SEM). Corrosion behavior was specified by
recording Potentiodynamic polarization curves and measuring the content of Ni ions, released into a SBF solution
using atomic absorption spectroscopy (AAS). Fourier transformation infrared radiation (FT-IR) and energy dispersive
spectroscopy were employed to verify the biocompatibility of the anodized and bare alloys after submersion in SBF. It
was shown that anodic oxidation in sulfuric acid significantly increases corrosion resistance and biocompatibility. This
layer improves corrosion resistance and Ni ion-release resistance by impeding the direct contact of the alloy with the
corrosion mediums i.e. Ringer and SBF solutions. The TiO2 oxide layer also decreases the releasing of Ni ions in to
SBF solution
M. Mahmoudiniya, Sh. Kheirandish, M. Asadi Asadabad,
Volume 14, Issue 1 (3-2017)
Abstract
Nowadays, Ni-free austenitic stainless steels are being developed rapidly and high price of nickel is one of the most important motivations for this development. At present research a new FeCrMn steel was designed and produced based on Fe-Cr-Mn-C system. Comparative studies on microstructure and high temperature mechanical properties of new steel and AISI 316 steel were done. The results showed that new FeCrMn developed steel has single austenite phase microstructure, and its tensile strength and toughness were higher than those of 316 steel at 25, 200,350 and 500°C. In contrast with 316 steel, the new FeCrMn steel did not show strain induced transformation and dynamic strain aging phenomena during tensile tests that represented higher austenite stability of new developed steel. Lower density and higher strength of the new steel caused higher specific strength in comparison with the 316 one that can be considered as an important advantage in structural applications but in less corrosive environment
A. Jafari Tadi, S.r. Hosseini, M. Naderi Semiromi,
Volume 14, Issue 3 (9-2017)
Abstract
Influence of formation of surface nano/ultrafine structure using deep rolling on plasma nitriding and tribological properties of the AISI 316L stainless steel was investigated. Initially, the deep rolling process was carried out on the bar-shaped specimens at 15 cycles with 0.2 mm/s longitudinal rate and 22.4 rpm bar rotation. Then, plasma nitriding treatment was applied on the as-received and deep rolled kinds at 450 °C and H2-25% Vol. N2 gas mixture for 5 h. Surface micro-hardness and un-lubricated pin-on-ring sliding wear tests were carried out on the as-received, deep rolled, plasma nitrided and deep rolled-plasma nitrided kinds. Results revealed that deep rolled-plasma nitrided kind is shown the highest wear resistance than the others, due to the further increased surface hardness achieved via the combined process.
Y. Dewang, M.s. Hora, S.k. Panthi,
Volume 14, Issue 4 (12-2017)
Abstract
Finite element simulation of stretch flanging process was carried out in order to investigate the effect of process parameters on maximum thinning (%) in stretch flanging process. Influences of initial flange length, punch die clearance, width of sheet metal blank and blank holding force were investigated on maximum thinning (%). Finite element simulation was done using FEM software package ABAQUS. Sheet metal blanks of AA 5052 were utilized for numerical simulation of stretch flanging process. Mesh convergence study was carried out to ascertain the accuracy of present FEM model. It is found that circumferential strain and shell thickness decreases with decrease in initial flange length and punch-die clearance while both decreases with increase in blank-holding force. Radial strain increases with decrease in initial flange length and punch-die clearance and with increment in blank-holding force and width of sheet. It is found that width of sheet metal blank and blank holding force have greater influence on maximum thinning (%) as compared to initial flange length and punch die clearance.
H. Fathi, B. Mohammad Sadeghi, E. Emadoddin, H. Mohammadian Semnani,
Volume 16, Issue 3 (9-2019)
Abstract
Abstract
In the present research, the behavior of 304L austenitic stainless steel in the deep drawing process has been studied at the room temperature through experimental and finite element simulation method. Magnetic method calibrated by XRD was used to measure induced-martensite. Martensite volume fraction in the various portion of the deep drawn cup under optimum Blank Holder Force (BHF) and in the rupture location was evaluated. Findings of the present study indicated that higher martensite volume fraction occurred in the flange portion in the drawn cup due to higher strain and stress concentration in this area. Also, rupture happened at the arc portion of the wall of drawn cup with higher blank diameter due to higher strain, work hardening and martensitic transformation. Both experimental and simulation results showed that maximum LDR of 2 obtained in the forming process. All experimental procedures were simulated by LS-DYNA software, employing MAT_TRIP, and experimental results were in good agreement with the FE simulation.
Mohammad Javad Sohrabi, Hamed Mirzadeh, Saeed Sadeghpour, Reza Mahmudi,
Volume 20, Issue 4 (12-2023)
Abstract
Deformation-induced α΄-martensite generally forms at shear bands in the coarse-grained austenite, while it nucleates at grain boundaries in the ultrafine-grained (UFG) austenite. The available kinetics models are related to the nucleation on the shear band intersections, and hence, their application to investigating the kinetics of α΄-martensite formation for the UFG regime cannot be justified. Accordingly, in the present work, the general Johnson–Mehl–Avrami–Kolmogorov (JMAK-type) model was implemented for comparing the kinetics of α΄-martensite formation in the UFG and coarse-grained regimes using an AISI 304L stainless steel. On the experimental front, the X-ray diffraction (XRD) patterns and the electron backscattered diffraction (EBSD) maps were used for phase and microstructural analyses, respectively. It was revealed that the simple JMAK-type model, by considering the dependency of the volume fraction of α΄-martensite on the strain, is useful for modeling the experimental data, predicting the nucleation sites based on the theoretical Avrami exponents, and characterizing the transformation kinetics at low and high strains.
