Rainer Traksmaa

Annealing effect for SnS thin films prepared by high-vacuum evaporation

Thin films of SnS are deposited onto molybdenum-coated soda lime glass substrates using the high-vacuum evaporation technique at a substrate temperature of 300 °C. The as-deposited SnS layers are then annealed in three different media: (1) H2S, (2) argon, and (3) vacuum, for different periods and temperatures to study the changes in the microstructural properties of the layers and to prepare single-phase SnS photoabsorber films. It is found that annealing the layers in H2S at 400 °C changes the stoichiometry of the as-deposited SnS films and leads to the formation of a dominant SnS2 phase. Annealing in an argon atmosphere for 1 h, however, causes no deviations in the composition of the SnS films, though the surface morphology of the annealed SnS layers changes significantly as a result of a 2 h annealing process. The crystalline structure, surface morphology, and photosensitivity of the as-deposited SnS films improves significantly as the result of annealing in vacuum, and the vacuum-annealed films are fo...

SEM analysis and selenization of Cu-Zn-Sn sequential films produced by evaporation of metals

The formation of Cu2SnZnSe4 thin films in the selenization of different sequential metallic and alloy films is investigated. It is shown that the main process of low temperature selenization (up to 300degC) is the formation of different binary copper selenides on the layer surface. High temperature selenization (over 400degC) leads to the formation of Cu2ZnSnSe4 phase with some excess of a separate ZnSe phase. The content of ZnSe diminishes with the rise of the selenization temperature, but the selenized films stayed always multiphased. The size of the formed Cu2ZnSnSe4 crystals is controlled by the composition of the precursor.

High-temperature erosion of Fe-based coatings reinforced with cermet particles

High-velocity oxy-fuel sprayed, iron alloy-based powder coatings, reinforced with tungsten carbide–cobalt (WC–Co) and titanium carbide–nickel molybdenum (TiC–NiMo) cermet particles, are compared under high-temperature abrasive–erosive wear conditions. Both WC–Co and TiC–NiMo particles underwent fracture, as well as dissolution, during the spraying process, but in the case of WC–Co particles this process was remarkably less intensive. Under the low impact angle conditions, the WC–Co particle-reinforced coating exhibited 1.1 times lower wear than the TiC–NiMo particle-reinforced coating because of the larger amount of the reinforcement remaining. Under the normal impact angle conditions, the WC–Co particle-reinforced coating showed 1.2 times lower wear than the TiC–NiMo particle-reinforced coating because of the resulting larger size of the WC–Co reinforcement and a more ductile matrix.

Processing of ZrC-TiC Composites by SPS

ZrC – TiC composites containing 20 wt.% TiC, along with and without 0.2 wt.% graphite were prepared by spark plasma sintering (SPS) at temperatures between 1600 - 1900 °C for 10 min under pressure up to 100 MPa. The addition of free carbon tends to reduce the appearance of tertiary phases in the microstructure according to scanning electron microscope (SEM) images. However, free carbon also reduced the mechanical properties of Vickers’ hardness and fracture toughness of the composites. SPS data showed when pressure was increased to 100 MPa, evident grain growth started to occur at a temperature as low as 1600 °C resulting in relative density > 100%. Samples produced at 1600 °C, but with maximum allowable pressure according to the SPS machine, yielded samples with greater hardness and fracture toughness compared to samples produced at 1900 °C.

Densification and Microstructure Development in Zirconia Toughened Hardmetals

Different process methods and parameters together with different amount of additives were used to fabricate WC-Ni-ZrO2 hardmetals with mechanical properties aiming at improved performance under erosive wear. XRD observation showed the presence of tetragonal zirconia in the cermet matrix after processing. The best erosion resistance with erosion rate of about 0.7 mm3/kg was demonstrated by the specimen produced either by vacuum sintering or SPS and added by 0.2 wt% of free carbon. This cermet has also demonstrated the highest hardness of 17.7 GPa.

Influence of the SPD Processing Features on the Nanostructure and Properties of a Pure Niobium

The structurization of a high purity niobium from double electron-beam melted cast microstructure to fine-grained microstructure was completed by equal-channel angular pressing by the Bc route up to a Von Mieses strain of 13.8. In addition, for the viscoplastic behavior study as well as nanostructure and properties improving the hard cyclic viscoplastic deformation, die forging at room temperature and followed heat treatment with low heating rate were conducted. The nanostructure of processed samples was characterized by transmission electron microscopy and X-ray diffraction testing. This paper focuses on several new trends in the study of improved mechanical and physical properties of pure niobium, to what purpose these materials will be used in industry. The crystallite size, microstrains and dislocation density in severe plastic deformed pure niobium were calculated and electric conduction was measured. The nanocrystalline microstructure with minimal crystallite size down to 62 nm as mean in cross-section of sample was received. By this the dislocation density varies from 5.0 E+10 to 2.0 E+11 cm-2 and was maximal for pure niobium which has minimal electrical conductivity, maximal value of hkl-parameter and maximal relative microstresses. The microhardness was maximal for sample after 12 passes by Bc route and for samples with 8 and 10 passes followed heat treatment at 170 and 350°C. The mechanisms answerable for the electronic conduction were discussed according to the microstructure evolution in the different directions and for different strain levels.

Reaction pathway to Cu2ZnSnSe4 formation in CdI2

We investigated various possible chemical interactions between individual precursor compounds (ZnSe, SnSe, and CuSe) and CdI2 as a flux material used in the CZTSe monograin powder synthesis–growth process in closed vacuum ampoules. The processes occurring in these mixtures were detected by the differential thermal analysis method. The phase changes in these processes were determined using X-ray diffraction and Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and mass spectrometry. The analyses showed that molten CdI2 was chemically active, forming Zn1−xCdxSe in the CdI2–ZnSe mixture by a chemical dissolution reaction; CdSe, SnI2 and SnI4 formed in the CdI2–SnSe mixtures and CdSe; and CuI formed in the CdI2–CuSe mixtures by exchange reactions.

Reaction pathway to Cu 2 ZnSnSe 4 formation in CdI 2

We investigated various possible chemical interactions between individual precursor compounds (ZnSe, SnSe, and CuSe) and CdI2 as a flux material used in the CZTSe monograin powder synthesis–growth process in closed vacuum ampoules. The processes occurring in these mixtures were detected by the differential thermal analysis method. The phase changes in these processes were determined using X-ray diffraction and Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and mass spectrometry. The analyses showed that molten CdI2 was chemically active, forming Zn1−xCdxSe in the CdI2–ZnSe mixture by a chemical dissolution reaction; CdSe, SnI2 and SnI4 formed in the CdI2–SnSe mixtures and CdSe; and CuI formed in the CdI2–CuSe mixtures by exchange reactions.

Formation of Ca–Zn–Na phosphate bioceramic material in thermal processing of EDTA sol–gel precursor

In this study, investigation of the Ca–P–O, Ca:Zn–P–O, Ca:Na–P–O, and Ca:Zn:Na–P–O precursor gels prepared using EDTA as complexing agent and slightly different starting materials was performed. For this purpose, thermal decomposition of the gels was studied by TG/DTA-EGA/MS with following evolvement of H2O, CO2, NH3, and NOx gases. Besides, thermal decomposition products were characterized by Fourier transform infrared spectroscopy, X-ray diffraction analysis, and scanning electron microscopy. It was demonstrated that thermal decomposition of Ca–P–O acetate and Ca:Zn–P–O, Ca:Zn:Na–P–O acetate-nitrate gels is different. Thus, the results of thermal decomposition of Ca:Zn–P–O and Ca:Zn:Na–P–O gels showed that Zn and Na additives accelerate decomposition of the gels. In addition, Na substitution at Ca sites creates conditions for the formation of the orthophosphate composites at lower temperatures.

Comparison of Curvature and X-Ray Methods for Measuring of Residual Stresses in Hard PVD Coatings

Physical Vapour Deposition and PVD coatings are designed for several applications, from industrial to biomedical. Residual stresses, arising during coating deposition, have important effect on the coating’s service life as their influence to the mechanical and tribological properties. Our aim was to investigate the residual stresses in five different PVD coatings (TiN, TiCN, TiAlN, TiAlN, nc-(AlTi) N/α -Si3N4) (presence of the Ti as adhesion layer) by the layer growing curvature method and the X-ray diffraction techniques using a plate and a strip as the substrate. Residual stresses were compressive and very large (2.98 - 7.24) GPa in all coatings and comparable in TiN, TiAlN, TiAlN coatings in the case of both methods. The magnitude of residual stresses is influenced by intrinsic strain in the case of layer growth rather than by thermal stress.