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Savko Malinov - One of the best experts on this subject based on the ideXlab platform.
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titanium alloys after surface gas nitriding
Surface & Coatings Technology, 2006Co-Authors: A. Zhecheva, Savko MalinovAbstract:Abstract Experimental studies using differential scanning calorimetry (DSC) for nitriding of four titanium-alloys near α Ti–8Al–1Mo–1V, near α Ti–6Al–2Sn–4Zr–2Mo, α + β Ti–6Al–4V and near β Ti–10V–2Fe–3Al at different temperatures and for different periods of time are presented. The X-ray diffraction (XRD) technique was used in order to study the phase transformations that occur during gas nitriding. As a result of the nitrogen interaction, a nitrided layer was formed that consists of titanium nitrides, followed by an interstitial solution of nitrogen in the hcp α titanium phase. The microstructural changes of these alloys in relation to the alloy composition and processing parameters were studied. It was found that the microstructure of alloys nitrided at temperatures below their β transus temperatures for various periods of time is uniform and homogeneous. With the increase of the temperature above their β transus temperatures the microstructure changes to irregular. Microindentation hardness testing using a Knoop indenter was conducted on the nitrided titanium alloys to analyse their hardness evolution in relation to the nitriding processing parameters and alloy composition. It was found that the microhardness increases with the increase of the temperature and time of nitriding. The surface morphology of the Ti–6Al–2Sn–4Zr–2Mo alloy in relation to the nitriding processing parameters was analysed.
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titanium alloys after surface gas nitriding
Surface & Coatings Technology, 2006Co-Authors: A. Zhecheva, Savko MalinovAbstract:Abstract Experimental studies using differential scanning calorimetry (DSC) for nitriding of four titanium-alloys near α Ti–8Al–1Mo–1V, near α Ti–6Al–2Sn–4Zr–2Mo, α + β Ti–6Al–4V and near β Ti–10V–2Fe–3Al at different temperatures and for different periods of time are presented. The X-ray diffraction (XRD) technique was used in order to study the phase transformations that occur during gas nitriding. As a result of the nitrogen interaction, a nitrided layer was formed that consists of titanium nitrides, followed by an interstitial solution of nitrogen in the hcp α titanium phase. The microstructural changes of these alloys in relation to the alloy composition and processing parameters were studied. It was found that the microstructure of alloys nitrided at temperatures below their β transus temperatures for various periods of time is uniform and homogeneous. With the increase of the temperature above their β transus temperatures the microstructure changes to irregular. Microindentation hardness testing using a Knoop indenter was conducted on the nitrided titanium alloys to analyse their hardness evolution in relation to the nitriding processing parameters and alloy composition. It was found that the microhardness increases with the increase of the temperature and time of nitriding. The surface morphology of the Ti–6Al–2Sn–4Zr–2Mo alloy in relation to the nitriding processing parameters was analysed.
Kojiro F. Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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An effective joint of continuous SiC/Ti-6al-4v composites by diffusion bonding
Composites Engineering, 1995Co-Authors: Shinji Fukumoto, Akio Hirose, Kojiro F. KobayashiAbstract:Abstract The continuous SiC/Ti-6al-4v composite was fabricated through a hot pressing procedure. Solid state diffusion (SSD) and transient liquid phase (TLP) bonding processes were applied to join continuous SiC/Ti-6al-4v composites to a Ti-6al-4v plate and to themselves. The butt joint strength of the composite to the Ti-6al-4v plate reached a maximum of approximately 850 MPa for V f = 30% composite. The maximum strength is 90% of the tensile strength of the Ti-6al-4v alloy. When the composite was bonded directly to itself, a sound joint was not obtained. A joint strength equal to composite Ti-6al-4v's joint strength was obtained using Ti-6al-4v and Ti-Cu-Zr thin foils as filler metal. However, a fracture occurred not at the base metal but at the bonding interface. Scarf joint forms were also used to join a composite to a Ti-6al-4v plate and to itself. When the scarf angle was less than 12°, the composite-composite joint strength reached a maximum value of 1380 MPa corresponding to 80% tensile strength of the base material. The composite-composite scarf joint was fractured at base material. The composite-Ti-6al-4v scarf joint was also fractured at the Ti-6al-4v plate when the scarf angle was less than 12°. It is possible to join the SiC/Ti-6al-4v composite without any reinforcing parts, such as a doubler.
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Diffusion bonding of SiC/Ti-6al-4v composite to Ti-6al-4v alloy and fracture behaviour of joint
Materials Science and Technology, 1993Co-Authors: Shinji Fukumoto, Akio Hirose, Kojiro F. KobayashiAbstract:AbstractContinuous SiC fibre reinforced Ti–6Al–4V composites were diffusion bonded to Ti–6Al–4V alloy. Bondability and the fracture mechanism of the joint were investigated. The joint strength increased with bonding time, and was a maximum at 850 MN m−2 for Vf=30% composite and 650 MN m−2 for Vf=45% composite. The bonding was completed sooner for Vf=30% composite than for Vf=45% composite. In Vf=30% composite, the maximum joint strength was about 85% of the tensile strength of Ti–6Al–4V. The void ratio at the interface between matrix and Ti–6Al–4V alloy decreased as bonding time increased. The joint strength was controlled by the bonding between the composite matrix and the Ti–6Al–4V alloy. The maximum joint strength was 100–150–MN–m−2 higher than the strength simply calculated from the area fraction of the bonded matrix/Ti–6Al–4V interface. Fibres were debonded from the matrix and the defects were produced around fibres, so the state of stress at the bond interface is triaxial owing to the defects and/or...
H. Shibata - One of the best experts on this subject based on the ideXlab platform.
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The effects of gas nitriding on fatigue behavior in titanium and titanium alloys
Journal of Materials Engineering and Performance, 1999Co-Authors: Keiro Tokaji, Takeshi Ogawa, H. ShibataAbstract:Fatigue behavior has been studied on gas-nitrided smooth specimens of commercial pure titanium, an alpha/beta Ti-6al-4v alloy, and a beta Ti-15Mo-5Zr-3Al alloy under rotating bending, and the obtained results were compared with the fatigue behavior of annealed or untreated specimens. It was found that the role of the nitrided layer on fatigue behavior depended on the strength of the materials. Fatigue strength was increased by nitriding in pure titanium, while it was decreased in the Ti-6al-4v and Ti-15Mo-5Zr-3Al alloys. Based on detailed observations of fatigue crack initiation, growth, and fracture surfaces, the improvement and the reduction in fatigue strength by nitriding in pure titanium and both alloys were primarily attributed to enhanced crack initiation resistance and to premature crack initiation of the nitrided layer, respectively.
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the effect of gas nitriding on fatigue behaviour in titanium alloys
International Journal of Fatigue, 1994Co-Authors: H. Shibata, Takeshi Ogawa, Keiro Tokaji, Chiaki HoriAbstract:Abstract The fatigue behaviour of gas-nitrided Ti6Al4V alloy and Ti15Mo3Al alloy has been studied under rotating bending, and the results obtained were compared with those for annealed or untreated materials on the basis of detailed observations of crack initiation, growth and fracture surfaces. Nitriding was performed using smooth specimens for 4 h and 15 h at 850°C in Ti6Al4V alloy and for 20 h and 60 h at 750°C in Ti15Mo5Zr3Al alloy in pure nitrogen gas. The depths of the nitrided layers obtained were approximately 25 μm and 65μm for the former, and 130 μm and 200 μm for the latter. In Ti6Al4V, the fatigue lives of the material nitrided for 4 h were shorter than those of the corresponding annealed material, but the fatigue limit was increased. However, fatigue strength was reduced by nitriding for 15 h. Similar results were obtained in Ti15Mo5Zr3Al: fatigue strength was decreased by nitriding for 20 h, and the fatigue lives of the material nitrided for 60 h were shorter than those of the annealed material, but the fatigue limit was slightly increased. The reduction in fatigue strength of the nitrided materials in both alloys was primarily attributed to premature crack initiation in the nitrided layer. The role of the nitrided layer in crack initiation is also discussed in terms of results for pure titanium in a previous report.
Reji John - One of the best experts on this subject based on the ideXlab platform.
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Ultrasonic assessment of additive manufactured Ti-6al-4v
2018Co-Authors: Norman Schehl, Vicki Kramb, Josiah Dierken, John C. Aldrin, Edwin J. Schwalbach, Reji JohnAbstract:Additive Manufacturing (AM) processes offer the potential for manufacturing cost savings and rapid insertion into service through production of near net shape components for complicated structures. Use of these parts in high reliability applications such as those in the aerospace industry will require nondestructive characterization methods to ensure post-process material quality in as-built condition. Ultrasonic methods can be used for this quality verification. Depending on the application, the service life of AM components can be sensitive to the part surface condition. The surface roughness and layered structure inherent to the electron-beam powder-bed fusion process necessitates new approaches to evaluate subsurface material integrity in its presence. Experimental methods and data analytics may improve the evaluation of as-built additively manufactured materials. This paper discusses the assessment of additively manufactured EBM Ti-6al-4v panels using ultrasonic methods and the data analytics applied to evaluate material integrity. The assessment was done as an exploratory study as the discontinuities of interest in these test samples were not known when the measurements were performed. Water immersion ultrasonic techniques, including pulse-echo and through transmission with 10 MHz focused transducers, were used to explore the material integrity of as-built plates. Subsequent destructive mechanical tests of specimens extracted from the plates provided fracture locations indicating critical flaws. To further understand the effect of surface-roughness, an evaluation of ultrasonic response in the presence of as-built surfaces and with the surface removed was performed. The assessment of additive manufactured EBM Ti-6al-4v panels with ultrasonic techniques indicated that ultrasonic energy was attenuated by the as-built surface roughness. In addition, feature detection was shown to be sensitive to experimental ultrasonic parameters and flaw morphology.Additive Manufacturing (AM) processes offer the potential for manufacturing cost savings and rapid insertion into service through production of near net shape components for complicated structures. Use of these parts in high reliability applications such as those in the aerospace industry will require nondestructive characterization methods to ensure post-process material quality in as-built condition. Ultrasonic methods can be used for this quality verification. Depending on the application, the service life of AM components can be sensitive to the part surface condition. The surface roughness and layered structure inherent to the electron-beam powder-bed fusion process necessitates new approaches to evaluate subsurface material integrity in its presence. Experimental methods and data analytics may improve the evaluation of as-built additively manufactured materials. This paper discusses the assessment of additively manufactured EBM Ti-6al-4v panels using ultrasonic methods and the data analytics applied...
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Fretting fatigue crack analysis in Ti–6Al–4V
International Journal of Fatigue, 2005Co-Authors: A. L. Hutson, Ted Nicholas, Reji JohnAbstract:Abstract A study was conducted to verify the efficacy of a fracture mechanics methodology to model the crack growth behavior of fretting fatigue-nucleated cracks obtained under test conditions similar to those found in turbine engine blade attachments. Experiments were performed to produce cracked samples, and fretting fatigue crack propagation lives were calculated for each sample. Cracks were generated at 106 cycles (10%-of-life) under applied stress conditions previously identified as the fretting fatigue limit conditions for a 107 cycle fatigue life. Resulting cracks, ranging in size from 30 to 1200 μm, were identified and measured using scanning electron microscopy. Uniaxial fatigue limit stresses were determined experimentally for the fretting fatigue-cracked samples, using a step loading technique, for R=0.5 at 300 Hz. Fracture surfaces were inspected to characterize the fretting fatigue crack front indicated by heat tinting. The shape and size of the crack front were then used in calculating ΔKth values for each crack. The resulting uniaxial fatigue limit and ΔKth values compared favorably with the baseline fatigue strength (660 MPa) for this material and the ΔKth value (2.9 MPa√m) for naturally initiated cracks tested at R=0.5 on a Kitagawa diagram. Crack propagation lives were calculated using stress results of FEM analysis of the contact conditions and a weight function method for determination of ΔK. Resulting lives were compared with the nine million-cycle propagation life that would have been expected in the experiments, if the contact conditions had not been removed. Scatter in the experimental results for fatigue limit stresses and fatigue lives had to be considered as part of an explanation why the fatigue life calculations were unable to match the experiments that were modeled. Analytical life prediction results for the case where propagation life is observed to be very short experimentally were most accurate when using a coefficient of friction, μ=1.0, rather than for the calculations using μ=0.3
A. Zhecheva - One of the best experts on this subject based on the ideXlab platform.
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titanium alloys after surface gas nitriding
Surface & Coatings Technology, 2006Co-Authors: A. Zhecheva, Savko MalinovAbstract:Abstract Experimental studies using differential scanning calorimetry (DSC) for nitriding of four titanium-alloys near α Ti–8Al–1Mo–1V, near α Ti–6Al–2Sn–4Zr–2Mo, α + β Ti–6Al–4V and near β Ti–10V–2Fe–3Al at different temperatures and for different periods of time are presented. The X-ray diffraction (XRD) technique was used in order to study the phase transformations that occur during gas nitriding. As a result of the nitrogen interaction, a nitrided layer was formed that consists of titanium nitrides, followed by an interstitial solution of nitrogen in the hcp α titanium phase. The microstructural changes of these alloys in relation to the alloy composition and processing parameters were studied. It was found that the microstructure of alloys nitrided at temperatures below their β transus temperatures for various periods of time is uniform and homogeneous. With the increase of the temperature above their β transus temperatures the microstructure changes to irregular. Microindentation hardness testing using a Knoop indenter was conducted on the nitrided titanium alloys to analyse their hardness evolution in relation to the nitriding processing parameters and alloy composition. It was found that the microhardness increases with the increase of the temperature and time of nitriding. The surface morphology of the Ti–6Al–2Sn–4Zr–2Mo alloy in relation to the nitriding processing parameters was analysed.
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titanium alloys after surface gas nitriding
Surface & Coatings Technology, 2006Co-Authors: A. Zhecheva, Savko MalinovAbstract:Abstract Experimental studies using differential scanning calorimetry (DSC) for nitriding of four titanium-alloys near α Ti–8Al–1Mo–1V, near α Ti–6Al–2Sn–4Zr–2Mo, α + β Ti–6Al–4V and near β Ti–10V–2Fe–3Al at different temperatures and for different periods of time are presented. The X-ray diffraction (XRD) technique was used in order to study the phase transformations that occur during gas nitriding. As a result of the nitrogen interaction, a nitrided layer was formed that consists of titanium nitrides, followed by an interstitial solution of nitrogen in the hcp α titanium phase. The microstructural changes of these alloys in relation to the alloy composition and processing parameters were studied. It was found that the microstructure of alloys nitrided at temperatures below their β transus temperatures for various periods of time is uniform and homogeneous. With the increase of the temperature above their β transus temperatures the microstructure changes to irregular. Microindentation hardness testing using a Knoop indenter was conducted on the nitrided titanium alloys to analyse their hardness evolution in relation to the nitriding processing parameters and alloy composition. It was found that the microhardness increases with the increase of the temperature and time of nitriding. The surface morphology of the Ti–6Al–2Sn–4Zr–2Mo alloy in relation to the nitriding processing parameters was analysed.
