Diffusion Of Substrate Elements Research Articles

The effects of substrate dilution on the microstructure and wear resistance of PTA Cu-Al-Fe aluminium bronze coatings

Cu-Al-Fe aluminium bronze alloys are good candidates for precious tools and forming dies due to their high wear resistance, good sliding properties and low tendency for adhesion to ferrous metals. Plasma transferred arc (PTA) is an effective process for deposition of such robust coatings by enhancing the bond between the bronze coating and steel substrate. However, the microstructure and wear characteristics of these coatings are strongly influenced by the diffusion of substrate elements (mostly iron) to the interface. In the present study, the effects of substrate dilution on the microstructure and wear behaviour of Cu-Al-Fe alloy deposited by PTA on medium carbon steel substrate were investigated. The results show that the deposition current controls the melting temperature and iron dilution which result in the formation of Cu3Al martensitic β1' phase in a low dilution and the ordered β1 phase in high dilution. The wear behaviour of the coating is dominated by failure of the matrix phase. Low dilution coating with martensitic phase exhibits the highest wear resistance. On high diluted Fe rich coating, pile up of dislocation on the intermetallic K phase leads to surface cracks and delamination of the coating resulting in a high wear rate.

HIGH-TEMPERATURE OXIDATION OF HOT-DIP ALUMINIZED P23 STEEL

ASTM P23 steel (Fe-2.25Cr-1.6W-0.1Mo in wt.%) was hot-dip aluminized and oxidized at 800∘C and 1000∘C for 20 h in air in order to determine the effect of aluminizing on the microstructure, hardness, and oxidation resistance of P23 steel. Aluminizing effectively increased the oxidation resistance of P23 steel by forming protective [Formula: see text]-Al2O3 scales. During oxidation, outward diffusion of substrate elements and inward transport of Al and oxygen occurred simultaneously. The oxidation and interdiffusion formed voids in the coating, lowered the microhardness, and transformed the original (Al-rich topcoat)/(Al[Formula: see text]Fe4 layer) to either (thin [Formula: see text]-Al2O3 scale)/(Al5Fe2 layer)/(AlFe layer)/(AlFe3 layer)/([Formula: see text]-Fe(Al) layer) at 800∘C or (thick [Formula: see text]-Al2O3 scale)/(AlFe3 layer)/([Formula: see text]-Fe(Al) layer) at 1000∘C. At 1000∘C, Fe2O3 was also formed in addition to [Formula: see text]-Al2O3 scale, due to the enhanced outward diffusion of Fe, thus suppressing the formation of cracks in the coating.

Influence of iron on the performance of CIGS thin-film solar cells

In the last years steel foil has become an attractive candidate for use as a flexible substrate material for Cu(Inx,Ga1−x)Se2 thin-film solar cells (CIGS). It is stable at the high temperatures present during CIGS processing and is also commercially available. However, one disadvantage is the diffusion of substrate elements into the CIGS layer, which are detrimental for the performance of solar cells. We found a direct correlation between the iron (Fe) content in the CIGS layer and corresponding solar cell parameters. A deep defect related to Fe impurities could be detected by admittance spectroscopy measurements. The solar cell parameters could be well fitted by simulation with recombination at an acceptor like deep defect in the bulk of the CIGS layer. The simulated density of deep defect states correlates nicely with the Fe concentration in the CIGS layer. From this we conclude that Fe replaces an In (or Ga) site in the CIGS lattice and creates an FeIn2+ (or FeGa2+) deep acceptor state in the bulk of CIGS layers, which is detrimental already at a low concentration in the sub ppm range. The simulations enabled us to estimate the maximum Fe concentration in CIGS layers which is tolerable without disturbing the performance of high-efficiency CIGS solar cells.

Structural and phase transformations on spark-laser coatings under fretting corrosion in air

The structure and phase transformations on the surface of a ZrB2-based combined laser–spark coating on titanium alloy are studied. The transformations are induced by triboprocesses under fretting corrosion in air. It is shown that the surface transformations result from a combination of three mechanisms: plastic deformation (surface texturing, fatigue, crack formation, brittle fracture); oxygen diffusion from the environment, chemical reactions of tribooxidation, diffusion of substrate elements (Al) toward the wear surface; and removal of particles from the surface. Two-phase nanostructured eutectic is found on the wear surface of the combined coating.

Cyclic Oxidation Behavior of IN 718 Superalloy in Air at High Temperatures

Ni-base superalloy IN 718 was cyclically oxidized in laboratory air at temperatures ranging from 750 to 950 °C for up to 12 cycles (14 h/cycle). The kinetic behaviour as well as the surface morphology, and the oxide phases of the scales were characterized by means of weight gain measurements, cyclic oxidation kinetics, scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) analysis techniques. The results showed that as the oxidation temperature increased, the oxidation rate, the external scale thickness, and internal oxidation zone increased. It was suggested that the oxidation rate was controlled by the diffusion of substrate elements in the alloy and the inward diffusion of oxygen through the oxide scale. The oxidation kinetics followed a sub-parabolic rate law and, the activation energy of oxidation was 249 ± 20 kJ mol−1. The scaling process was controlled mainly by the diffusion of chromium, titanium, manganese, and oxygen ions through the chromia scale. IN 718 showed low weight gain and very slow reaction rates of substrate elements at 750 °C. At 850 °C, a continuous and very thin oxide scale was formed. At 950 °C, XRD and EDS-elemental mapping analysis revealed that a complex oxide scale had formed. It consisted of an outermost layer of TiO2–MnCr2O4 spinels, inner layer of Cr2O3, and the inner most layer composed of Ni3Nb enriched with Nb, Ti and Al oxides underneath the chromia layer. The oxide scale at this temperature seemed to be thicker layer, significant spallation and volatilization had apparently occurred, and greater internal corrosion was identified. The doping effect of titanium was observed, where it was found to be diffused through the chromia scale to form TiO2 at the oxide-gas interface as well as internally and at the oxide alloy interface. The amount of rutile (TiO2) at the oxide surface increased with temperature. In view of Mn contents in the alloy, the manganese–chromium spinel oxide was inferred to have played an important role in cyclic oxidation behaviour of IN 718, where the change in oxidation kinetic was noted. The Al contents would cause internal Al-rich oxide formation at grain boundaries.

Topographical analysis by 3-D profilometry in the study of the oxidation of Cr–N coated hard metal tools

Abstract Conventionally oxidation studies involve thermogravimetric analysis, in which the weight gain is related to the oxide formation. In this work, the oxidation of 4 μm and 7 μm Cr–N coated hard metal tools was monitored using the 3-D profilometry, in conjunction with XRD, EDS and SEM analyses. For oxidation tests at 850 °C in air, a higher weight gain was observed for 4 μm Cr–N system. After oxidation, XRD detected chromium and tungsten oxides for the thinner film system, whereas only chromium oxide was observed for the other. Nevertheless, SEM and EDS results indicated that Cr and W oxides exist on both systems. During oxidation process, besides the outward diffusion of Cr and a probably outward diffusion of substrate elements, such as W, the inward diffusion of oxygen also occurred in some degree through the films, with O 2 reaching the substrate and forming tungsten oxide. This process generated a volumetric expansion, which resulted in local adhesion loss and film rupture. These results indicated that, on coated systems oxidation studies, the weight gain could be not only related with film oxidation, but also with film and substrate oxidation.

Adhesion of TiC and Ti(C,N) coatings on steel

The scratch test has been used to measure the adhesion of CVD TiC coatings on various steels by comparing the critical load factors. The critical load (Lc) of a coating–substrate interface determined by the scratch test depends not only on the adhesion but also the substrate hardness and coating thickness. For identical deposition conditions, the coating thickness depends strongly on the carbide forming elements in the steel. In this work, a careful separation of these effects has allowed us to quantify the adhesion of a given system from the critical load. Of the nine steels tested, two had improved adhesion which was shown to be caused by diffusion of substrate elements into the coating. Adhesion measurements of Ti(C,N) coatings deposited by PVD are discussed and compared to the adhesion values of CVD TiC on the same steel substrates.