Solid State Phenomena Vol. 191

Abstract: The aim of the studies was to determine the oxidation kinetics of two magnesium alloys, i.e. WE43 and MSR-B, in CO2 atmosphere with and without the addition of 2 vol.% H2O. The rate of oxidation was measured by thermogravimetry in the temperature range of 530-580°C, i.e. below and above the eutectic melting point. The melting point of the eutectic mixture was determined by differential scanning calorimetry (DSC). The corrosion products were analysed by scanning electron microscopy (SEM) and X-ray microanalysis combined with EDS. Studies showed that on the WE43 alloy, a two-layer scale was formed, in which the outer part was composed of yttrium and magnesium oxides, while the inner part contained only yttrium oxide. The scale was found to preserve its good protective properties even above the eutectic temperature. Analysis of the results showed that on the MSR-B alloy, under a thin, uneven layer of scale, the process of internal oxidation occurred, and at a temperature of 580°C, the alloy underwent partial melting

Abstract: The purpose of this study was to evaluate resistance to galvanic and crevice corrosion of magnesium alloys AZ61 and AZ80. Resistance to galvanic corrosion was evaluated with additional application of aluminium alloy 2017A and 8Mn2Si steel as reference materials. The tests were carried out by means of potentiostat VoltaLab PGP 201 by Radiometer with application of Evans method. The tests were carried out in the solution with concentration of 0.01 M NaCl in ambient temperature. For comparison, the relations of the surface of magnesium alloys to aluminium alloys and steel (1:1, 5:1 i 10:1) was differentiated in the experiment. It was proved that AZ80 alloy features slightly higher corrosion resistance in contact with aluminium alloy and steel.

Abstract: Magnesium alloys of Mg-Y-RE-Zr series are characterized by creep resistance up to a temperature of 250 ° C, and can work up to a temperature of 300oC. These properties allow for the application of alloys of Mg-Y-RE-Zr series for the elements of racing car engines operating in the conditions of high loads and temperatures. The requirement of high reliability components of aircraft propulsion system, with high strength and corrosion resistance, also led to the use of these alloys in the aerospace industry. Welding technologies in cast magnesium alloys are applied in order to repair defects in castings, occurring in the casting process, as well as to regenerate worn out castings. Joints made of magnesium alloys should have at least the same properties as a finished casting. The literature lacks information on the properties of joints welded of cast magnesium alloys.This work includes examination of influence of heat treatment on creep resistance of alloy WE43. Material for the study comprised joints made by the TIG method, welded in the cast state. Creep tests were carried out on joints without heat treatment and joints after heat treatment. The tests were performed at the temperatures of 200 ° C and 250 ° C during 100h. It was found that there is an increase in creep resistance of the joints after heat treatment.

Abstract: The QE22 cast magnesium alloy containing silver, rare earth elements and zirconium is characterized by high mechanical properties and creep resistance of up to 200 ° C. It is cast gravitationally into sand moulds and permanent moulds. After the casting process any possible defects appearing in the cast are repaired with the application of welding techniques. The repaired cast should possess at least the same properties as the one which does not require any repairs. The aim of this thesis was to determine the impact of the heat treatment on the microstructure of the QE22 alloy welded joint. The creep resistance of the welded joints was also analyzed.

Abstract: Metal matrix composites comprising a magnesium matrix and Mg₂Si/MgO dispersoids obtained by hot pressing silica nanoparticle agglomerates and metal powder in a Degussa press were characterized. Two powder mixtures having weight proportions of Mg:SiO₂ of 10:0.3 and 10:1 were identically sintered. Their microstructures were characterized by optical microscopy and X-ray diffraction. The size and distribution of the Mg₂Si and MgO dispersoids formed in situ were assessed as a function of the original nanosilica content. The behaviour of the composites under compression testing was assessed in 3D by X-ray microtomography using 225kV Nikon X-tek and 150kV Xradia MicroXCT scanners. This provided insights into composite strengthening mechanisms and matrix particle decohesion.

Abstract: Metal matrix composite comprising a multiphase magnesium matrix and titanium particles fabricated by hot pressing was characterized. Powder mixture of the Mg:Ti:Al at weight ratio equal to 10.5:6.1:3.4 was sintered at 640, 650 and 660°C whereas other parameters were held constant. Thermal effects during heating and cooling of powder mixture were measured by differential scanning calorimetry (DSC). Microstructure of composite was characterized by scanning electron microscopy (SEM) with a use of X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). For all conditions of components consolidation α-Mg, α-Ti, Mg₁₇Al₁₂ and Al₃Ti were identified. It was revealed that dispersion and location of Mg₁₇Al₁₂ and Al₃Ti compounds depended on sintering temperature. Measurements of hardness and density of obtained non-porous composite gave approximate results of 130 HV and 2.7 g/cm³ respectively

Abstract: In this paper, the technology of melting in induction furnaces with ceramic crucibles was used for production of TiAl-based Ti-47Al-2W-0.5Si alloy. Due to high reactivity of liquid titanium alloys, the melting process was conducted in special crucibles made of stabilised ceramic materials resistant to the aggressive action of these alloys. When characterising the chemical composition and microstructure of Ti-47Al-2W-0.5Si alloy melted in different ceramic crucibles, problems accompanying the melting process were described and conditions for making an alloy with satisfactory purity were determined.

Abstract: In this paper, the possibility of refining grain of Ti-48Al-2Cr-2Nb alloy in the processes of multi-stage heat treatment consisted of initial heat treatment, cyclic heat treatment and under-annealing was evaluated. Microstructural changes that take place during the particular heat treatment procedures were also described. It was demonstrated that due to the application of combined cyclic heat treatment and under-annealing almost 24-fold grain refinement in relation to the state after homogenising could be obtained. Probable mechanisms of grain refinement in the proposed heat treatment processes were also presented and influence of individual procedures of the proposed treatment on selected properties of the investigated alloy was described

Abstract: This paper presents the results of testing the corrosion resistance of pure Ti and Ti6Al4V alloy improved by carbon addition at the level of 0.2 and 0.5 wt.%. The testing was carried out at room temperature in HNO3 acid solution (40%) and HCl acid solution (5 and 10%). It has been established that carbon addition affects the improvement in electrochemical corrosion resistance of pure Ti and Ti6Al4V alloy in HNO3 solution, whereas the higher carbon content the better corrosion resistance of Ti. For Ti6Al4V alloy the increase in corrosion resistance is caused by carbon addition at the level of 0.2 wt.%. The result of the corrosion resistance of both pure Ti and Ti6Al4V alloy with carbon in a solution of HCl indicates that the more detrimental is the solution of lower concentration

Abstract: Influence of hydrogen on the structure of titanium alloys is a complex phenomenon, depending on the circumstances, may be negative or positive [1,2]. The presence of hydrogen in titanium alloys usually results in degradation of their microstructure and properties, as well promote some undesirable effects such as hydrogen corrosion and hydrogen embrittlement [3]. Positive nature of the effects of hydrogen on the properties of titanium alloys is manifested in the high temperature hydrogen treatment (HTM - Hydrogen Treatment of Materials), where hydrogen is temporary alloying component [4-9]. This is possible because of the high values of diffusion coefficients can be easily introduced into the titanium and it just as easily removed. Titanium and its alloys show the absorbability of almost 60 at. % of hydrogen at 600°C. The limit hydrogen of solubility in Tiα is very low and does not exceed 0.05 at. % at room temperature. The limit hydrogen of solubility in Tiβ is much higher and its maximum value is 48 at. %. Since the beginning of the titanium industry, a great deal of attention has been paid to control the hydrogen content at titanium products – above 0.2 ppm. The paper presents the results of the possibilities of hydrogen using as a temporary alloying element in Ti-6Al-4V alloy. Treatment of hydrogen alloy consisted of three stages: hydrogenation in hydrogen gas atmosphere at 650 °C, a cyclic hydrogen-treatment (3 cycles 650 °C to 250 °C) and a dehydrogenation in vacuum (550 °C). It was shown that hydrogen affects appreciably changes the microstructure of surface layer of the tested titanium alloy. The aim of this study is thus to determine the effect of hydrogen on the two-phase microstructure, hardness, and surface fracture of the titanium alloy Ti-6Al-4V due to high-temperature hydrogen treatment.