Made available in DSpace on 2014-10-09T12:36:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:00Z (GMT). No. of bitstreams: 1 04366.pdf: 5734662 bytes, checksum: 226af9141e1984ce9dff1230b5f437ed (MD5) / Tese (Doutoramento) / IPEN/T / University of Manchester, England

Made available in DSpace on 2014-10-09T12:31:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:56:06Z (GMT). No. of bitstreams: 1 01363.pdf: 907419 bytes, checksum: 885bb5e2ea74ebae7dd9dd5a5d958871 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

No description available.

Nanoindentation technique was used to investigate the surface properties of A2 and D2 tool steel subjected to different heat treatments. the mechanical characteristics of these two easily available tool steels were studied based on microstructural images obtained from SEM, the grain growth after heat treatment using X-ray diffraction method and nanoindentation technique. the investigation showed that a single nanoindentation result can explain how heat treatment influences reliability and failure in A2 and D2 tool steels. in this work, the causes and effects of these variations were studied to explain how they influence reliability and failure in A2 and D2 tool steel. Finally, a cube-corner indenter tip was used to determine the fracture toughness of silicon wafer. the emphasis of this research is on how nanoindentation technique is more extensive in material characterization.

No description available.

Yes / Mechanical properties of 2-4% manganese PM steels were determined in tension and in bending following laboratory sintering in dry, hydrogen rich atmospheres. Young's modulus determined by an extensometric technique was about 115 GPa; when measured by an ultrasonic method it was about 153 GPa, in accordance with the 'law of mixtures'. The microstructures, significantly devoid of oxide networks, were predominantly pearlitic, but frequently with variability for specimens similarly processed, resulting in appreciable variations in the stresses for macroscopic yielding and fracture. The majority of the experiments were conducted on 3 and 4Mn-0·6C alloys and for these R0·1 was in the range 275-500 MPa, tensile strength (TS) 300-600 MPa, and (apparent) transverse rupture strength (TRS) 640-1260 MPa. Statistical techniques were employed to analyse the data. When careful control of processing was maintained, the Weibull modulus was highest, at about 17, for TS of furnace cooled specimens, and lowest, about 6, for TRS of the rapidly cooled specimens. In order to interpret the significant differences between the TRS and the TS values, both apparently measuring the critical stress for cracking after strains of up to 7%, a two stage normalising technique for TRS was adopted. By taking account of the plastic strains preceding failure, the elastic 'strength of materials' formula was modified to allow true fracture stresses to be calculated. It was also postulated that failure was initiated from a population of flaws of variable size and then the 'normalised' bend strengths, smaller than TRSs, were shown to correspond well with TSs. It is suggested that this combined plasticity correction and Weibull analysis approach, which has a sound scientific basis, should be employed to interpret bend test data in preference to empirical correlations between TS and TRS.

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Made available in DSpace on 2014-10-09T12:44:30Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:21Z (GMT). No. of bitstreams: 1 06907.pdf: 7394695 bytes, checksum: bde9c680792583e55f4754af5867fe98 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Maraging steels have got high strength and good toughness. Maraging steel MDN 250A grade is used for slat tracks on the leading edge of the wing of Light Combat Aircraft (LCA). This application requires high strength and good wear resistance. Required wear resistance for this application can be achieved by ion-nitriding (also called as Plasma nitriding or Glow discharge nitriding) process of case hardening. In conventional gas nitriding process the nitriding temperature is 500 – 550 0C, which is above the aging temperature of maraging steel. Ion-nitriding at temperatures lower than 480 0C is thought to be suitable for surface hardening for application of this material in slat tracks of the leading edge of the wing of LCA. Besides this ion-nitriding is stated to improve fatigue & wear resistance properties without significantly affecting other properties. Also this is a process where the thickness requirement is minimum for the wear properties accomplished. Further, no distortion, warpage and such other dimensional inhomogeneity problems are encountered. In ion-nitriding method glow discharge technology is used to introduce nascent (elemental) nitrogen to the surface of a metal part for subsequent diffusion into the material. The plasma assisted surface modification techniques offer a great flexibility and are capable in tailoring desirable chemical and structural surface properties independent of the bulk properties. It has other advantages like nil or very thin white layer after nitriding and there is no machining or grinding involved for complex parts after the process. The hardened surface layers become an integral part of the basic material without any significant reduction in the properties of base material. Aim of the present work is to study ion-nitriding process on Maraging steels, to carry out ion nitriding of Maraging steel MDN 250A grade at different temperatures and evaluation of properties. Presently, the ion-nitrided slat tracks have been cleared for limited usage instead of full expected life. Studies are also needed to understand the fatigue behavior upon nitriding. The main aspects considered in this study are, optimization of thickness of the ion-nitrided layer and properties required for aircraft applications like slat tracks on the leading edge of the wing where wear resistance, corrosion resistance, mechanical properties like tensile strength, impact strength and fatigue strength are important. To establish the variation in the basic properties of maraging steel (MDN 250A Grade) because of ion nitriding. Aging of Maraging steel is done at 480 ± 5 0C with very close temperature control. In industrial ion-nitriding furnaces the temperature control is of the order of ± 10 0C. As a part of this research work ion-nitriding at three different temperatures which are well below 480 0C were chosen. These temperatures are 435 0C, 450 0C and 465 0C and soaking time i.e., ion-nitriding duration is 10 hours. Microstructure is characterized using optical microscope, scanning electron microscope and X-ray Diffraction. Properties evaluated include Hardness, Case depth, Tensile, Low Cycle Fatigue, Impact and Corrosion by Salt Spray. Optical microscopy and SEM examination don’t show change in core microstructure of the material after ion-nitriding. The iron compound formed in the hardened layer is Fe4N for all the three nitriding temperatures. Ion-nitrided specimens exhibit higher surface hardness and good case depth. Salt spray test results shows that there is animprovement in corrosion resistance after nitriding. The nitrided samples shown higher UTS and 0.2 % PS values than un nitrided ones, where as % Elongation and % Reduction in Area are lower for nitrided samples as compared to un nitrided samples. This can be attributed to the surface layer getting hardened because of ion nitriding. Impact strength of nitrided samples is lower compared to un nitrided samples. This is again due to the surface layer getting hardened because of ion nitriding. Low cycle fatigue properties obtained on ion-nitrided samples show improvement in the fatigue strength due to introduction of the residual compressive stresses. The mechanical properties satisfy the design requirements. Thus ion-nitriding of this Maraging steel (MDN 250A Grade) is suitable for parts which are subjected to constant wear and are complex in shape.

Made available in DSpace on 2014-10-09T12:54:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:42Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP