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The interest in using high vacuum-compatible time-of-flight secondary ion mass spectrometry (TOF-SIMS) detectors integrated within focused ion beam instruments (FIB) has increased due to the possib...

Nanocrystalline (nc) alloys are stronger than their coarse-grained versions. Here, we report ultrastrong alloys, discovered via high-throughput screening of the nc CoCr33-69 materials library. The nc materials library was fabricated using magnetron co-sputtering. The alloys consist of textured, columnar structures with grain size in the nanometric regime. We found that the texture and phase composition can be tailored by changing the Cr concentration. In the investigated region of the nc CoCr system, a relatively broad spectrum of yield strength, determined via micropillar compression tests, was found ranging from 1.41 GPa up to 3.64 GPa. The remarkable strength increment was caused by a chemically- and thermally-driven phase and microstructure evolution of the system. The strongest alloys were found in the regions containing the δCoCr phase, which was considered previously as metastable. Density functional calculations revealed that the δCoCr phase is more energetically favourable in Cr-rich regions compared to single-phase simple solid solutions (HCP, BCC). Experimental results showed that the range of its occurrence is wider than previously thought, i.e. after annealing the δCoCr phase was found above 44 at. % of Cr. We demonstrate that systematic screening of materials libraries can boost the discovery of new materials with outstanding properties.

The present work was undertaken to determine the effect of nickel on the microstructure in rapidly solidified ∼ Fe-25Cr-xNi-5Mo-0.8C alloys. The alloys were synthesised via arc melting and rapidly solidified using the suction casting technique. Phase composition was investigated using synchrotron x-ray diffraction and the solidification range was determined by means of differential scanning calorimetry. The microstructure in as-cast state was analysed using scanning electron microscopy. Properties were investigated by hardness measurements and scratch tests using the nanoindentation technique. The obtained results were discussed with respect to thermodynamic calculations, carried out using the CALPHAD approach. It was observed that with increasing nickel contents the average dendrite size, mean free path of the matrix and the spacing between the lamellar carbides, as well as the regularity and thickness of the carbides decreased. With decreasing mean free path of the matrix a decrease of average scratch depth occurred. This corresponds to abrasive wear, i.e. in alloys having smaller average dendrite size, abrasive particles will more frequently encounter eutectic areas with greater hardness than the matrix. As a result, the material exhibits greater abrasive wear resistance. The results presented in this work show that there is a possibility to enhance abrasive wear resistance of hypoeutectic iron-based alloys by modifying their chemical composition and, in turn, reducing the mean free path of the matrix.

In the present work, the concept of hypoeutectic Fe-Cr-Ni-Mo-C alloys additionally strengthened by the Frank-Kasper phases is shown. The alloys were designed using the CALPHAD approach in order to obtain a matrix with high corrosion resistance, similar to that of stainless steels, and good wear resistance at room and elevated temperatures, achieved by the precipitation of eutectic carbides and the Frank-Kasper phases. The main design strategy is to produce alloys with a narrow solidification range and precipitations of the Frank-Kasper phases within the dendrites after heat treatment in order to reduce the mean free path of the matrix. The effect of molybdenum on the evolution of intermetallic phases in the Fe-25Cr-xMo-0.8C system was determined. Additionally, the influence of nickel in the Fe-25Cr-5Mo-xNi-0.8C system on phase composition of the matrix, as well as the stability and volume fraction of intermetallic phases were investigated. Lever-Rule and the modified Scheil-Gulliver solidifications were simulated for selected five alloys in order to investigate the phase precipitation sequence. Particular emphasis during the discussion was placed on the influence of Mo and Ni on phase stability, as well as solidus and liquidus temperatures in the investigated systems.

A novel Zn-3Ag-0.5Mg alloy was plastically deformed using 3 processing paths: hot extrusion (HE), HE followed by cold rolling (CR) and high-pressure torsion (HPT). The processed samples consisted of the η-Zn phase, ε-Zn3Ag precipitates within the matrix, and nanometric Zn2Mg precipitates within the Zn11Mg2 phase located at the grain boundaries. Both the η-Zn phase and Mg-rich phases were enriched in Ag. Electron backscattered diffraction was used to examine the effects of grain size and texture on mechanical behavior with tensile tests performed at room temperature (RT) at different strain rates. The coarse-grained (~ 6 µm) samples after HE exhibited high strength with brittleness due to dislocation interaction with dispersed precipitates and, to some extent, with twinning activation. Significant grain refinement and processing at RT gave an increase in elongation to over 50 pct in CR and 120 pct in HPT. Ductile CR samples with an average grain size of ~ 2 µm and favorable rolling deformation texture gave a yield strength of ~ 254 MPa, a tensile strength of ~ 456 MPa, and a reasonable strain rate sensitivity. These values for the CR samples meet the mechanical requirements for biodegradable stents in cardiovascular applications.

The fabrication of high-hardness non-hydrogenated diamond-like carbon (DLC) via standard magnetron sputtering (MS) is often hindered by the low sputtering yields and ionisation rates of carbon, therefore investigations into pulsed alternatives of MS, else sputtered species post-ionisation methods, are of particular interest. This work focuses on investigating the influence of pulsed-direct current MS (pDCMS), high power impulse magnetron sputtering (HiPIMS) and their microwave plasma-assisted (MA-pDCMS, MA-HiPIMS) variants on the properties of the fabricated DLC films. Two setups were used for the pDCMS- and HiPIMS-based methods, respectively. The films were characterised using Raman spectroscopy, nanoindentation, X-ray reflectometry and scanning electron microscopy, where the pDCMS-produced films were additionally characterised by film-stress measurements. Moreover, in situ time-resolved Langmuir probe plasma analysis was performed under HiPIMS and MA-HiPIMS conditions to analyse the influence of the magnetron and microwave plasmas on one another. For both DCMS- and HiPIMS-based procedures, it was found that the addition of microwave plasma did not facilitate attaining hardnesses beyond 30 GPa, however, it did enable modifying the morphology of the films. Furthermore, this study shows the potential of synchronised sputtering with substrate biasing, as well as the importance of microwave plasma source positioning in relation to the substrate.

In this paper, the concept, microstructure and properties of the Ni-Cr-Ta-Al-C complex phase alloy are presented. The alloy was designed to work at elevated temperatures, in a chemically aggressive environment and under harsh wear conditions. The alloy was examined in an as-cast state and after heat treatment using a number of complementary techniques such as: scanning electron microscopy, 3D reconstruction by means of focused ion beam-scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nanoindentation, dilatometry, hardness measurements and in-situ tensile tests at elevated temperatures. The microstructure of the alloy is comprised of a dendritic chromium-rich nickel-based matrix, which is strengthened by spheroidal precipitations of the γ’ Ni3(AlTa) phase as well as Chinese script-like TaC and Cr7C3 carbides. Analysing hardness and microstructural changes of the alloy after solution treatment and after aging in different conditions allows to optimise the alloy's heat treatment procedure. It was found that the alloy achieved the highest hardness values after aging at 800 °C, which is related with the evolution of the γ’ phase. Additionally, it was discovered that primary carbides are stable up to at least 1150 °C, which is promising from the viewpoint of working at elevated temperatures and under harsh wear conditions. The herein reported results show that the combination of eutectic carbides and ordered γ’ phase for strengthening and, possibly, improving wear resistance of the alloy is effective up to at least 850 °C.

In this work, vibrating sample magnetometry was used to analyse and correlate the magnetisation versus temperature behaviour in the metastable, hypoeutectic Fe-Cr-C alloy with the evolution of the intradendritic segregation, especially chromium depleted regions, as a consequence of applied heat treatment. The Fe-24.5-0.79C alloy used in this work was synthesised in a suction casting device under a high purity argon atmosphere. The investigated alloy contains chromium-rich carbides (paramagnetic phase) and a Fe-Cr solid solution (ferromagnetic phase) in the form of primary and secondary dendrites. The microstructure of the alloy was investigated in the as-cast state and after heat treatment for 4 h at 650, 800 and 1000 °C using scanning electron microscopy and atomic force microscopy, while the evolution of the domain structure was determined by magnetic force microscopy. The occurrence of chromium depleted regions in the rapidly solidified alloy was confirmed using energy-dispersive X-ray spectroscopy, as well as magnetisation measurements by means of vibrating sample magnetometry. It was found that the chromium depleted regions with a width below 1.5 μm, found in the suction cast rod, disappear after heat treatment for 4 h at temperatures greater than 800 °C. Magnetic measurements and behaviour analysis of the Curie temperature, herein reported, exhibit volumetric character and were successfully applied to detect the chromium depleted regions, as well as to qualitatively evaluate the effect of heat treatment on homogenisation in the investigated alloy.

This paper presents a comprehensive study on the strain-induced martensitic transformation and reversion transformation of the strain-induced martensite in AISI 304 stainless steel using a number of complementary techniques such as dilatometry, calorimetry, magnetometry, and in-situ X-ray diffraction, coupled with high-resolution microstructural transmission Kikuchi diffraction analysis. Tensile deformation was applied at temperatures between room temperature and 213 K (−60 °C) in order to obtain a different volume fraction of strain-induced martensite (up to ~70 pct). The volume fraction of the strain-induced martensite, measured by the magnetometric method, was correlated with the total elongation, hardness, and linear thermal expansion coefficient. The thermal expansion coefficient, as well as the hardness of the strain-induced martensitic phase was evaluated. The in-situ thermal treatment experiments showed unusual changes in the kinetics of the reverse transformation (α′ → γ). The X-ray diffraction analysis revealed that the reverse transformation may be stress assisted—strains inherited from the martensitic transformation may increase its kinetics at the lower annealing temperature range. More importantly, the transmission Kikuchi diffraction measurements showed that the reverse transformation of the strain-induced martensite proceeds through a displacive, diffusionless mechanism, maintaining the Kurdjumov–Sachs crystallographic relationship between the martensite and the reverted austenite. This finding is in contradiction to the results reported by other researchers for a similar alloy composition.

This paper presents the effect of high temperature heat treatment on the evolution of eutectic carbides and on the M7C3 → M23C6 carbides reaction in the rapidly solidified hypoeutectic Fe-Cr-C alloy. The investigated alloy was designed using the CALPHAD approach via ThermoCalc in order to obtain a high volume fraction of eutectic carbides with high thermodynamic stability and matrix, where BCC to FCC phase transformation is shifted to temperatures above 1100 °C. The Fe-Cr-C alloy was synthesized in an arc furnace in a high purity argon atmosphere. The studies involved a wide range of experimental techniques to characterize the alloy in the as-cast state, after heat treatment for 4 h at 650, 800 and 1000 °C and during continuous heating including in-situ high temperature X-ray diffraction, high-resolution dilatometry, light microscopy, scanning electron microscopy, transmission electron microscopy and microhardness tests. The microstructure of the investigated alloy in the as-cast state is composed of primary dendrites with secondary branches of Fe-Cr solid solution with eutectic, very fine, rod-like M7C3 (M = Cr and/or Fe) as the predominant carbides and a small amount of M23C6 carbides. It was found that during heating, the M7C3 → M23C6 transformation proceeds in the temperature range between 500 and 600 °C. The first stage of the carbides transformation is the uphill diffusion of chromium from the matrix into M7C3, which is reflected in the abnormal growth of lattice parameters above 400 °C. When the chromium concentration in M7C3 achieves the required level, the orthorhombic M7C3 carbide transforms in-situ into the equilibrium cubic M23C6 carbide with a higher symmetry of the crystal structure. Additionally, the effect of heat treatment on the eutectic carbides' morphology evolution was determined. The M7C3 → M23C6 transformation results in a significant increase in the final volume fraction of carbides, which enhances the coalescence process of rod-like carbides.

In the present study, experimental and thermodynamic analysis of phase transformation in hypoeutectic Fe–24Cr–11Ni–4Mo–0.64C alloy is presented. The investigated alloy was synthesized in an arc furnace in high-purity argon atmosphere using suction-casting unit. Chemical composition of the alloy was determined using an optical emission spectrometer. The microstructure was characterized by scanning electron microscopy. Phase composition in as-cast state was analysed by X-ray diffraction and compared with thermodynamic calculations for equilibrium state using Thermo-Calc software. The analysis of phase transformations was conducted by dilatometry and differential scanning calorimetry investigations. It was found that phase composition of the alloy after non-equilibrium solidification (cooling rate ~30 °C s−1) differs significantly from equilibrium state. Critical temperatures of phase transformations in the alloy were determined.

The aim of the study was to synthesize and characterize the selected in-situ composites from the Fe-Cr-Ni-Mo-C system, additionally strengthened by intermetallic compounds. The project of the alloys was supported by thermodynamic simulations using Calculation of Phase Diagram approach via Thermo-Calc. Selected alloys were synthesized in an arc furnace in a high purity argon atmosphere using a suction casting unit. The studies involved a range of experimental techniques to characterize the alloys in the as-cast state, including optical emission spectrometry, light microscopy, scanning electron microscopy, electron microprobe analysis, X-ray diffraction and microhardness tests. These experimental studies were compared with the Thermo-Calc data and high resolution dilatometry. The results of investigations presented in this paper showed that there is a possibility to introduce intermetallic compounds, such as χ and σ, through modification of the chemical composition of the alloy with respect to Nieq and Creq. It was found that the place of intermetallic compounds precipitation strongly depends on matrix nature. Results presented in this paper may be successfully used to build a systematic knowledge about the group of alloys with a high volume fraction of complex carbides, and high physicochemical properties, additionally strengthened by intermetallic compounds.

An influence of two different cooling rates on the microstructure and dispersion of the components of high-entropy alloy from Al-Ti-Co-Ni-Fe system has been examined. For investigated alloys, the effective partitioning coefficient has been calculated. This factor indicates the degree of segregation of elements and allows for the specification of the differences between dendrites and interdendritic regions. The obtained results allow for the conclusion that the cooling rate substantially affect the growth of dendrites and the volume fraction of interdendritic regions as well as the partitioning of elements in the alloy. Furthermore, the obtained results made it possible to compare the influence of the cooling rate and the chemical composition on the dispersion of the alloying elements.

Microstructural and microchemical characterization of Ni-Ta-Al-Cr-C coating layer, deposited by Gas Tungsten Arc Welding (GTAW) method on AISI 310 is presented. The layer was characterized by X-ray diffraction (XRD), light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and hardness measurements. Results obtained by XRD and TEM show that the coating layer consists of a γ-nickel matrix strengthened by the γ′-Ni3(Al,Ta) phase, MC and M7C3 carbides (of tantalum-and chromium-rich type, respectively). Growth mechanism, which depends on the cooling rate determines morphology of eutectic carbides. For slow growth rate MC carbides tend to be blocky, while for greater growth rate they exhibit a tendency to form more developed shapes. M7C3 carbides have a polygonal and reticulated plate morphology with different sizes. The γ′-Ni3(Al,Ta) phase has a spherical shape with few nanometers in diameter. The average hardness of the AISI 310 substrate is 174 ± 5 HV1, while the hardness of Ni-Ta-Al-Cr-C coating layer is 359 ± 31 HV1.

The paper presents the results of the characterization of alloy from Fe-Cr-C (carbon content 0.79 wt.%) system including the microstructure, phase analysis, morphology and hardness in as cast state. The chemical composition was designed to create chromium-rich ferritic matrix with high volume fraction of carbides in form of interdendritic eutectics. The research was carried out on the cross section of the ingot, synthesized in an arc furnace under high purity argon atmosphere and crystallized on water-cooled copper mould. Microstructural characterization was carried out by light microscopy and scanning electron microscopy (SEM). Phase identification was performed by X-Ray diffraction (XRD). The microstructure of the investigated alloy is composed of primary and secondary dendrites Fe-Cr solid solution and complex M23C6and M7C3carbides in interdendritic areas. Segregation of Cr and C during crystallization causes precipitation of M7C3carbides. The average hardness of the alloy is 205±12 HV10.

Crystallography and Morphology of Chromium Rich Eutectic Carbides in an As-Cast Fe–Cr–C Alloy Crystallized in Non-Equilibrium Conditions K. Wieczerzaka,∗, P. Bala, T. Tokarski and M. Gajewska AGH University of Science and Technology, Faculty of Metals Engineering and Industrial Computer Science, al. A. Mickiewicza 30, 30-059 Krakow, Poland AGH University of Science and Technology, Academic Centre for Materials and Nanotechnology, al. A. Mickiewicza 30, 30-059 Krakow, Poland