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  • 1.
    Babushkin, O.
    et al.
    Luleå tekniska universitet.
    Harrysson, Ralph
    Luleå tekniska universitet.
    Herbertsson, H.
    Luleå tekniska universitet.
    Lindbäck, Ture
    Morphological effect of Al2O3 additives on sinterability of wear-resistant AlN ceramics1990Ingår i: Structural ceramics processing, microstructure and properties: proceedings of the 11th Risø International Symposium on Metallurgy and Materials Science, 3-7 September 1990 / [ed] J.J. Benzen, Roskilde: Risø National Laboratory , 1990, s. 175-180Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the present study on AlN-based ceramic materials, an attempt was made to show the morphological influence of the precursors on the phase relationships during sintering as well as the microstructural development of the material. An investigation has been done of the phase transformations during pressureless sintering of wear-resistant ceramics based on the AlN-Al2O3-Y2O3 system in the AlN-rich field as well as a study of the effect of different precursors, such as Al2O3, AlCl3 and Al(NO3)3, on the sequence of phase transitions in the low temperature field (800-1400°C). The peculiarities of phase transitions in dynamic and isothermal schedules have also been discussed.

  • 2.
    Babushkin, O.
    et al.
    Luleå tekniska universitet.
    Harrysson, Ralph
    Luleå tekniska universitet.
    Lindbäck, Ture
    Tegman, R.
    Luleå tekniska universitet.
    High-temperature graphite furnace for X-ray powder diffraction1993Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 4, nr 8, s. 816-819Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A modified computer-controlled high-temperature x-ray diffractometer with good stability and an upper temperature limit of more than 2300 K is described. A critical test of the system, determining the thermal expansion of Pt, Ni and AlN, showed close agreement with dilatometric and literature data. Lattice thermal expansion data of CrB2 and TiB2 up to 2100 K were also determined

  • 3.
    Babushkin, Oleg
    et al.
    Luleå tekniska universitet.
    Harrysson, Ralph
    Luleå tekniska universitet.
    Lindbäck, Ture
    Effect of sintering atmosphere and alumna precursors on the sequence of solid state reactions i the AlN-Y2O3-Al2O3 system1993Ingår i: Third Euro-ceramics conference: Madrid; 12-17 Sept. 1993 / [ed] P. Duran; J.F. fernandez, Faenza Editrice Iberica , 1993, Vol. vol. 1, s. 1079-1084Konferensbidrag (Refereegranskat)
    Abstract [en]

    High temperature x-ray diffraction was used to investigate the evolution of phases at 1050 C in three AlN-based ceramic powder mixtures containing Al2O3 and Y2O3 additives. The overall composition was 87.5 mol% AlN, 10% Al2O3 and Y2O3 2.5%; the alumina precursors in the three mixtures were Al2O3, AlCl3 and Al(NO3)3 respectively. The effects of the tape of precursor and the heat treatment atmosphere (vacuum or nitrogen) on the phases formed and the sequence of their formation over a period of two hours, are presented and discussed.

  • 4.
    Harrysson, Ralph
    Luleå tekniska universitet.
    Laser drilling of ceramic materials: energy distribution and crack development1991Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 5.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Herbertsson, Harald
    Luleå tekniska universitet.
    Energy distribution during laser machining of glass1988Ingår i: Lasers in manufacturing: proceedings of the 5th international conference, LIM-5, 13-14 September 1988, Stuttgart, West Germany / [ed] Helmut Hügel, IFS , 1988, s. 25-34Konferensbidrag (Refereegranskat)
    Abstract [en]

    Hole drilling of glass has been performed by use of a pulsed CO sub 2 laser of type Rofin Sinar RS 1500 in order to determine the best conditions for laser drilling. Relations have been established between the specific energy, the power density and the pulse time needed for drilling holes through glass plates of defined thicknesses. From these relationships it has been possible to decide the correct laser parameters for an optimized hole drilling with minimized crack formation

  • 6.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Herbertsson, Harald
    Luleå tekniska universitet.
    Grundläggande studier av trämaterials brottmekaniska egenskaper kontra mikrostruktur1989Rapport (Övrigt vetenskapligt)
  • 7.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Herbertsson, Harald
    Luleå tekniska universitet.
    Laser machining of HIP produced ceramics1988Ingår i: HIP: proceedings of the International Conference on Hot Isostatic Pressing, Luleå, 15-17 June 1987 / [ed] Tore Garvare, Luleå: CENTEK , 1988, s. 389-393Konferensbidrag (Refereegranskat)
    Abstract [en]

    HIP-produced high performance ceramics often need secondary machining. The investigation is concentrated on laser drilling of HIP-Si sub 3 N sub 4 and sialon using the single pulse technique. Experimental data give linear graphs for the specific energy vs. the pulse time and the power density vs. the inverse pulse time. The relationships are used for the construction of EP-diagrams, e.g. the relationship between specific energy and power density of the laser beam. From the EP-diagram can be found the energy consumption divided into different sources and different areas of machinability due to the power density

  • 8.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Herbertsson, Harald
    Luleå tekniska universitet.
    Laserbearbetning av högpresterande keramer 21987Rapport (Övrigt vetenskapligt)
  • 9.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Herbertsson, Harald
    Luleå tekniska universitet.
    Persson, S.
    Luleå tekniska universitet.
    Termisk etsning av glas med högeffektlaser1985Rapport (Övrigt vetenskapligt)
  • 10.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Lindbäck, Ture
    Vomacka, P.
    Luleå tekniska universitet.
    Crack formarion during laser machining of ceramics detected by acoustic emission1991Ingår i: Euro-Ceramics II / [ed] G. Ziégler; H. Hausner, DKG , 1991, Vol. Vol. 1, s. 671-675Konferensbidrag (Refereegranskat)
    Abstract [en]

    During laser machining of ceramics, cracks can occur in the material around the irradiated area. These cracks reduce the strength of machined parts and may possibly hinder their use as an engineering material. It is therefore very important to establish methods for the detection and avoidance of crack formation. As an aid for detecting crack formation, the acoustic emission method was used for two materials: soda lime glass and sialon. The results have led to the conclusion that it is possible to detect a signal coming from a crack in the investigated material and that the power of the detected signal is due to propagation of the crack. The relationship between laser parameters and crack formation was found with the aid of acoustic emission signal analysis. It was also found that it is possible to minimise or avoid crack formation by choosing suitable laser parameters

  • 11.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Vomacka, P.
    Luleå tekniska universitet.
    Acoustic emission response of soda lime glass after a single Nd-YAG laser pulse1994Ingår i: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 6, nr 3, s. 153-158Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When machining brittle solids with a laser, crack formation can occur in the material around the irradiated area causing a strength reduction of the machined material. The purpose of this work was to study a well known brittle material (soda lime glass) by means of acoustic emission (AE) in order to investigate the correlation between visually observed crack formation and detected AE energy released by the crack formation in the material. During and after irradiation of soda lime glass with an Nd-YAG laser pulse, the number of hits and amount of AE energy were measured in the first 300 s using AE. It was found that it is possible to detect AE signals from cracks caused by irradiation with a single Nd-YAG laser pulse. The power of the detected signal is related to the amount of crack formation. Cracks can be minimized or avoided by choosing a suitable combination of pulse time and power density of the single laser pulse. The cracks which occur after a laser shot extend mainly in the radial direction from the irradiated area.

  • 12.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Vomacka, P.
    Luleå tekniska universitet.
    Glass formation in the system Y2O3-Al2O3-SiO2 under conditions of laser melting1994Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 14, nr 4, s. 377-381Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Glass formation in the Y2O3---Al2O3---SiO2 system was investigated by means of laser melting using a CO2 laser source (wavelength 106 μm) with a maximum output power of 1700 W. The glass-forming region was found to be more extensive than that observed by other investigators. No glassy phase formed in compositions with less than 20 wt% SiO2. A non-equilibrium phase diagram corresponding to the conditions of laser-induced rapid melting and self-quenching was also determined. All the phases reported in the relevant binary diagrams with the exception of yttrium silicate 2Y2O3.3SiO2 were observed.

  • 13.
    Harrysson, Ralph
    et al.
    Luleå tekniska universitet.
    Vomacka, Peter
    Luleå tekniska universitet.
    Distanselement av kiselnitridbaserade keramer för användning vid elektrolytisk framställning av natriumklorat1993Rapport (Övrigt vetenskapligt)
  • 14.
    Navara, Erik
    et al.
    Luleå tekniska universitet.
    Harrysson, Ralph
    Luleå tekniska universitet.
    On the mechanism of austenite formation during inter-nd subcritical annealing of a C-Mn steel1984Ingår i: Scripta Metallurgica, ISSN 0036-9748, Vol. 18, nr 6, s. 605-610Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Austenite formation in low carbon-manganese steels upon intercritical annealing proceeds by nucleation and growth of the manganese-enriched phase accompanied by concurrent dissolution of the manganese-lean high-carbon austenite transformed from pearlite. When the annealing temperature is below the A 1 for the nominal Mn content, the austenite forms in the same way while pearlitic carbide dissolves. The rate controlling mechanism is the diffusion of manganese in ferrite, and it is likely that volume, grain-boundary as well as phase-boundary diffusion contribute to growth. The manganese content of the isothermally formed austenite is temperature dependent in an inverse way, rendering a high hardenability to steels treated at and below 725 degree C

  • 15.
    Vomacka, P.
    et al.
    Luleå tekniska universitet.
    Harrysson, Ralph
    Luleå tekniska universitet.
    Crystallization behavior and hardness of ZrO2-free and ZrO2-containing glass-ceramics in the system Y2O3-Al2O3-SiO21997Ingår i: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 26, nr 3, s. 132-138Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Y2O3 and Al2O3 are commonly used as sintering aids during sintering of silicon nitride based ceramics such as Si3N4 and sialon materials. These 2 oxides together with SiO2 present on the surface of Si3N4 particles form a liquid at elevated sintering temperatures and subsequently a glassy grain-boundary phase on cooling which causes a deterioration of the high temperature properties of the material. ZrO2 added to yttria-alumina-silica glasses is of interest as a potential nucleating agent which could shorten the incubation period of nucleation and increase the rate of nucleation. The objectives of the present study were to monitor the crystallization process in the Y2O3-Al2O3-SiO2 system by hardness measurements. Methods: A study has been made of the effect of crystallization on the hardness evolution in two glasses in the Y2O3-Al2O3-SiO2 system. The weight ratio of the three oxides in both glasses was 46.9:24.3:28.8 but one of the glasses was modified by the addition of 6 wt% ZrO2 which has a significant influence on the crystallization morphology. The progress of crystallization was monitored by means of X-ray diffractometry and by metallography. Results and conclusions: The crystalline phases in both materials were harder than the parent glasses but more so in the ZrO2 free material. The hardness increased with volume fraction crystallization but not linearly which suggests the influence of morphological factors such as crystal contiguity on hardness

1 - 15 av 15
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