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COATING OF CR-V LEDEBURITIC TOOL STEEL WITH CrAgN
Jurči, P. ; Krum, S. ; Dlouhý, Ivo
The Vanadis 6 tool steel has been coated with CrN, doped with small silver addition, by reactive magnetron sputtering. Some of coated specimens were subsequently vacuum annealed at 500 degrees C. The microstructure of film has been investigated on fracture surfaces of samples. Adhesion was evaluated by scratch-test. Wear resistance was measured using a pin-on-disc method, against alumina and 100Cr6 balls, at ambient and elevated temperatures. Experimental results have shown that the CrN-layers with an addition of 3%Ag have grown in a columnar manner. The addition of small amount of silver makes the adhesion on the substrate better. At an ambient temperature, no positive effect of the Ag-addition to the wear characteristics was found. But, in the testing temperature range 400 - 500 degrees C, significant lowering of friction coefficient and improvement of wear resistance were recorded. This can be attributed to the transport of Ag towards the surface, and thereby reduced friction force.
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AGEING OF BINARY Ti-Ni ALLOY AND ITS INFLUENCE ON TRANSFORMATION CHARACTERISTICS
Szurman, I. ; Kursa, M. ; Petlák, D. ; Dlouhý, Antonín
Transformation temperatures of binary alloys from Ti-Ni system are highly sensitive to chemical composition of the alloy. This sensitivity, however, causes rather considerable complications already during process of preparation. Transformation temperatures of bays rich in Ni can be successfully modified. The key to modification of transformation temperatures lies in use of precipitation reaction of quenched over-saturated solution for influencing of composition of TiNi matrix and thus to precise control of transformation temperatures. Principle of this method consists in metastable balance between intermetallic phase TiNi and coherent precipitates Ti3Ni4. Although the precipitate Ti3Ni4 is considered to be metastable in comparison with TiNi3, it is highly stable at temperatures below 600 degrees C. During precipitation reaction Ti3Ni4 is formed and this phenomenon is connected with decrease of Ni content in TiNi matrix, which leads to increased temperatures of phase transformations TR (temperature of formation of R-phase) and Ms (temperature 'martensite start'). It is important that transformation temperature after long-term ageing is independent on chemical composition of the alloy, and it depends only on temperature of ageing as a consequence of equilibrium between these phases. This phenomenon should not occur at ageing at higher temperatures, formation of precipitate Ti3Ni4 should occur only during cooling of the sample from the temperature of ageing. The alloy Ni50.6-Ti (at. %), prepared in high-frequency induction vacuum furnace, was chosen as experimental material. Samples of the alloy were sealed into evacuated quartz glass tube and aged at constant temperature with various durations of dwell. Afterwards transformation characteristics of the samples were determined by DSC method.
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STRUCTURAL, THERMODYNAMICS AND PHYSICAL PROPERTIES OF Zn Sn Al ALLOYS
Drápala, J. ; Musiol, J. ; Petlák, D. ; Vodárek, V. ; Smetana, B. ; Zlá, S. ; Kostiuková, G. ; Kroupa, Aleš ; Sidorov, V.E.
Some results of thermodynamic, structural and physical properties of Al-Sn-Zn alloys are presented in our paper. The ternary Al-Sn-Zn alloys were prepared in a resistance furnace in evacuated ampoules. The alloys were studied metallographically, their micro-hardness and X-ray micro-analysis (EDX, SEM) of individual phases were measured. Temperatures of phase transitions (liquidus, solidus, invariant reactions, etc.) were obtained using the DTA method (Setaram SETSYS 18 (TM)). The long time annealing (250, 300, 350 degrees C, 3, 7, 14 or 28 days) was used in order to achieve the thermodynamic equilibrium. The results were confronted with thermodynamic modelling of the ternary Al Sn Zn system in the Institute of Physics of Materials AS of the Czech Republic in Brno. We have studied density (by gamma-absorption method), electrical resistivity (by contactless method in rotating magnetic field) and magnetic susceptibility (by Faraday's method) of some Al-Sn-Zn alloys containing up to 10 at.% of aluminum and up to 65 at.% of zinc. The increasing of zinc content resulted in the decrease of the density and susceptibility values, except for one sample. The resistivity values practically didn't depend on the zinc content in the crystalline state, whereas a maximum was found for one of the samples in the liquid state. This work has been made in the frame of COST Action MP0602 project 'Advanced Solder Materials for High-Temperature Application'.
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