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Sökning: hsv:(TEKNIK OCH TEKNOLOGIER) hsv:(Materialteknik) > Malmö universitet

  • Resultat 1-10 av 264
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  • Areitioaurtena, Maialen, et al. (författare)
  • Numerical and experimental investigation of residual stresses during the induction hardening of 42CrMo4 steel
  • 2022
  • Ingår i: European journal of mechanics. A, Solids. - : Elsevier. - 0997-7538 .- 1873-7285. ; 96
  • Tidskriftsartikel (refereegranskat)abstract
    • The usage of induction hardening in the industry has increased in the last years due to its efficiency and repeatability. Induction hardening produces a hard martensitic layer on the specimen surface, which is accompanied by the generation of compressive residual stresses in the hardened case and tensile stresses in the untreated core. Residual stresses generated by induction hardening greatly impact on fatigue performance, as they act as crack growth retardants. In this work, a multiphysical coupled finite element model is developed to simulate induction hardening and compute the final residual stress state of the specimens along the microstructural transformations and hardness evolution. The impact of the transformation induced plasticity strain in the stress-state of the specimen during the process is also studied. The experimental validation shows that considering the transformation induced plasticity in induction hardening simulations improves the residual stress predictions, concluding that this effect should be included to achieve good residual stress predictions, especially in the subsurface region.
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  • Azadian, Saied (författare)
  • Aspects of precipitation in alloy Inconel 718
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • A study was made of the microstructure of the Ni-base alloy Inconel 718 with emphasis on the precipitation and stability of intermetallic phases as affected by heat treatments. In addition the effect of the precipitation on selected mechanical properties namely hardness, creep notch sensitivity and hot ductlity were investigated. The materials studied were a spray-formed version and three wrought versions of the alloy. The spray-formed version of the alloy was of interest since it exhibited a superior compositional homogeneity to more conventional forms of the alloy. To characterise the precipitation kinetics and to determine the associated hardening, a series of isothermal ageing treatments were carried out on both spray-formed and ring rolled material at selected temperatures between 600°C and 1025°C for up to 100h. The results were presented in the form of TTH diagrams for the two alloys. The heat treated specimens were then studied using optical microscopy, scanning electron microscopy and transmission electron microscopy. Where possible these were supplemented with quantitative metallographic measurements of volume fraction and precipitates size.The three main intermetallic precipitation phases in IN 718 are (i) gamma’ having a composition Ni3(Al,Ti), a cubic crystal structure and cubic or spherical particle shape (ii) gamma” having a composition Ni3Nb, a bct crystal structure and a lens-like disc shape (iii)delta having composition Ni3Nb, an orthorhombic crystal structure and forming as grain boundary particles and films as well as thin plates extending long distances into the grains. In thermomechanically processed material the delta-phase can also occur as shorter platelets and particles resulting from fragmentation of the original plates. In this work the rates of precipitation and the temperature ranges of their existence were determined qualitatively. Moreover the coarsening of the ganmma" precipitates was determined quantitatively. The kinetics of precipitation and dimensional coarsening of the delta-phase were also established quantitatively. Similarly, the dissolution kinetics of the delta-phase were measured in the spray-formed and three wrought versions of the alloy leading to a determination of the effect of Nb-content on the delta solvus temperature. After a standard heat treatment, the spray-formed IN 718 was found to be creep notch sensitive according to an SAE-AMS standard rupture test. It was found that notch ductility could be restored to the alloy by inserting a delta-phase precipitation treatment at 875°C-900°C prior to the standard heat treatment. This could be attributed to the formation of a more favourable delta-phase morphology than that formed during the solution treatment at 954°C in the standard heat treatment cycle. A study was made of high temperature tensile properties of a wrought version of IN 718 in particular in relation to the problem of hot cracking in repair welding. Measurements were made of the strength loss temperature on heating and the strength and ductility return temperatures on cooling. These properties provide an indication of the sensitivity of the alloy to hot cracking due to liquation. The tests were made on the alloy after various heat treatments designed to produce microstructures with two different grain sizes with and without delta-phase precipitation. Hot tensile tests were also performed on the in-situ solidified alloy in order to describe the weld metal ductility and properties. The grain size and the presence of large fractions of delta-phase precipitated at 900°C had only small effects on the strength loss temperature and brittle-ductile transition of the alloy. On the other hand, a small fraction of delta-phase precipitated in the grain boundaries at 960°C reduced the brittle-ductile transition temperature significantly. It is proposed that the reduction was associated with interaction between the grain boundary delta-phase and grain boundary boron segregation that was observed in all the heat treated materials.
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  • Pederson, Robert, et al. (författare)
  • Microstructure and mechanical properties of friction- and electron-beam welded Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo
  • 2012
  • Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 552, s. 555-565
  • Tidskriftsartikel (refereegranskat)abstract
    • This work presents mechanical data and microstructural characterization of friction welded (FRW) and electron beam welded (EBW) post weld heat treated (PWHT) specimens of Ti-6Al-2Sn-4Zr-6Mo and Ti-6Al-4V. PWHT Ti6246/Ti6246 welds and Ti64/Ti6246 welds were evaluated with tensile-, creep-. Charpy-V, and microhardness tests. The PWHT treatments were 593 degrees C/2 h, 640 degrees C/2 h and 704 degrees C/2 h, respectively. The microstructure of the different weld types and alloy combinations where examined and characterized using optical microscope and SEM. Tensile strength and yield strength were within specification for both material combinations. The elongation for Ti6246 welded to Ti6246 is below specification. Only small variations in tensile properties were found for the different PWHTs. Fracture occurred in base material of the Ti64 alloy for the combination of Ti64 welded to Ti6246. Charpy-V tests shows that the welds are more brittle compared with the base material. The largest difference was found in Ti6246 welded to Ti6246. No significant variation in creep properties for the different PWHTs has been found. Ti64 welded to Ti6246 shows poor creep properties due to the high testing temperature for the Ti64 alloy. Ti6246 welded to Ti6246 shows good creep properties compared to the base material. The general trend for the weld microhardness was a decreasing hardness with increasing PWHT temperature. One exception though was the FRW Ti64/Ti6246 combination, were the hardness of the Ti6246 side of the HAZ, close to the interface between the two alloys, was highest after a PWHT temperature of 593 degrees C, then decreasing in hardness for 640 degrees C, not PWHT and being least hard for the PWHT temperature of 704 degrees C. The hardness of the Ti64 base material showed no decrease after the PWHTs, but the hardness of the Ti6246 bulk material decreased after PWHT at 704 degrees C. (c) 2012 Elsevier B.V. All rights reserved.
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7.
  • Pederson, Robert (författare)
  • The microstructures of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo and their relationship to processing and properties
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The research described in the thesis concerns phase transformations and mechanical properties of the titanium alloys Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo. The need to weld the alloys for certain engine components can expose the alloy locally to non-optimum thermal cycles and it is therefore of importance to gain an understanding of the kinetics involved in the phase transformations during heating and cooling. Moreover, for the purpose of modelling and computer simulations of heat treatments and welding processes, quantitative descriptions of the transformation are necessary. One focus in this work has been to examine the feasibility of using high temperature X-ray diffraction (HT-XRD) to study the phase transformation kinetics. Another aim in this work was to develop a weld simulation model leading to a prediction of the joint structure and microstructure of an electron beam welded component of the alloy Ti-6Al-4V. Electron beam welding (EBW) and friction welding (FRW) of Ti-6Al-4V and Ti-6Al-2Sn-4Zr- 6Mo have also been investigated, including microstructural weld characterization and the effect of post weld heat treatments on selected mechanical properties. In addition, two components of Ti-6Al-4V produced by ring-rolling and closed die forging, respectively, showed unexpected differences in low cycle fatigue (LCF) under certain loading conditions. Quantitative metallographic studies and texture examinations were conducted in order to find possibly reasons for the observed difference in fatigue properties. The HT-XRD technique was successfully used to monitor the alpha-to-beta transition during heating and the beta-to-alpha transition during cooling and including the transformation kinetics during isothermal hold. From the recorded spectra the thermal expansion properties for the alpha and beta phases could be extracted up to a temperature of 1050C, enabling the determination of the overall thermal expansion for the alloy by using rule of mixture (ROM) calculations. The weld simulation model here presented proved to predict the joint structure and microstructure of an electron beam welded Ti64 component with reasonable good accuracy, both in terms of thermal history during welding and also in terms of martensitic fraction formed during cooling and the distribution of martensite through the cross section of the FZ and HAZ. All mechanically tested Ti64/Ti6246 EBWs and FRWs, independent of PWHT temperature, fractured in the Ti64 base material and not in the weld region, thus, both types of welding processes seem to be promising candidate methods for successful joining of the Ti64 alloy to the Ti6246 alloy. Quantitative metallographic studies revealed that the closed die forged material exhibited a finer primary alpha grain size and a finer Widmanstätten platelet colony size which would be expected to provide a superior resistance to fatigue crack initiation. Observed differences in the texture of the two materials as determined by electron back-scattered diffraction might also have contributed to the difference in fatigue properties.
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8.
  • Pettersen, Ketil, et al. (författare)
  • Creep Resistant Mg Alloy Development
  • 2000
  • Ingår i: Magnesium Alloys and their Applications. - Weinheim : John Wiley & Sons. - 9783527302826
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)
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  • Fisk, Martin, 1981-, et al. (författare)
  • Modelling of induction hardening in low alloy steels
  • 2018
  • Ingår i: Finite elements in analysis and design (Print). - : Elsevier. - 0168-874X .- 1872-6925. ; 144, s. 61-75
  • Tidskriftsartikel (refereegranskat)abstract
    • Induction hardening is a useful method for improving resistance to surface indentation, fatigue and wear that is favoured in comparison with through hardening, which may lack necessary toughness. The process itself involves fast heating by induction with subsequent quenching, creating a martensitic layer at the surface of the workpiece. In the present work, we demonstrate how to simulate the process of induction hardening using a commercial finite element software package with focuses on validation of the electromagnetic and thermal parts, together with evolution of the microstructure. Experiments have been carried out using fifteen workpieces that have been heated using three different heating rates and five different peak temperatures resulting in different microstructures. It is found that the microstructure and hardening depth is affected by the heating rate and peak temperature. The agreement between the experimental and simulated results is good. Also, it is demonstrated that the critical equilibrium temperatures for phase transformation is important for good agreement between the simulated and experimental hardening depth. The developed simulation technique predicts the hardness and microstructure sufficiently well for design and the development of induction hardening processes.
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