H11 hot work tool steel (1.2343) belongs to the most commonly used materials in the tooling industry, with significant heritage in producing extrusion dies or injection molds. Those components often are characterized by complex geometries, which makes them a great candidate for additive manufacturing. However, the hot working steel is hard to process by additive manufacturing technologies due to its cracking susceptibility related to high cooling rates occurring during printing. A potential way to reduce cracking tendencies is to utilize a point-by-point laser scanning methodology which influecnes the thermal conditions of the process. To prove this, a series of samples were produced via Powder Bed Fusion with various manufacturing parameters and without build platform preheating. Produced samples have been investigated by light and scanning electron microscopy methods, X-ray analysis, and hardness tests. The obtained results indicate that the use of short laser pulses in Powder Bed Fusion can limit the cracking in printed parts. In addition, the laser pulses play an important role in shaping the microstructure of the processed H11 hot work tool steel. The optimal parameters limiting the crack density to 6 mm−2 with 0.1 % porosity in H11 steel printouts were determined.
Abstract In the following work presents results of high carbon alloys from the Ni-Ta-Al-M system are presented. The alloys have been designed to have a good tribological properties at elevated temperatures. Despite availability of numerous hot work tool materials there is still a growing need for new alloys showing unique properties, which could be used under heavy duty conditions, i.e. at high temperatures, in a chemically aggressive environment and under heavy wear conditions. A characteristic, coarse-grained dendritic microstructure occurs in the investigated alloys in the as-cast condition. Primary dendrites with secondary branches can be observed. Tantalum carbides of MC type and graphite precipitations are distributed in interdendritic spaces in the Ni-Ta-Al-C and Ni-Ta-Al-C-Co alloys, while Tantalum carbides of MC type and Chromium carbides of M 7 C 3 type appeared in the Ni-Ta-Al-C-Co-Cr and Ni-Ta-Al-C-Cr alloys. In all alloys g’ phase is present, however, its volume fraction in the Ni-Ta-Al-C and Ni-Ta-Al-C-Co alloys is small. During heating from as-cast state in Ni-Ta-Al-C and Ni-Ta-Al-C-Co alloys, the beginning of the tantalum carbides precipitation process (MC type) followed (or simultaneous) by the intermetallic phase precipitation (g’ – Ni 3 (AlTa)) was stated, while in Ni-Ta-Al-C-Co-Cr and Ni-Ta-Al-C-Cr alloys, besides Tantalum carbides also the Chromium carbides precipitation occurred. It means that the investigated alloys were partially supersaturated in as-cast state. Above 1050°C in all investigated alloys the g’ phase is dissolving. In addition, the precipitation of secondary carbides during slow cooling was occured.
In this work, the effect of topologically close-packed χ phase on the microstructure and properties of the rapidly solidified hypoeutectic iron-based Fe-25Cr-7Mo-0.8C alloy was investigated. The novelty of the work is based on the introduction of χ phase into the Fe-based hypoeutectic alloy with the aim of reducing the mean free path of the matrix and increasing abrasive resistance. The phase composition was studied using in situ neutron and ex situ X-ray synchrotron diffraction. The microstructural evolution was analyzed via scanning and transmission electron microscopy and modelled using CALPHAD thermodynamic calculations. The mechanical behavior of the evolving microstructure was quantified using high-speed nanoindentation mapping. At low temperatures (650 °C), the χ phase nucleates mainly in dendrite areas and exhibits a needle-like morphology caused by high misfit with the ferritic matrix. At higher temperatures (800 °C), the χ phase nucleates on carbide/matrix interfaces and in dendrites and is characterized by a blocky morphology. Simultaneously, the evolution of M23C6 carbide morphology towards a continuous and solid network of precipitates was observed. Such changes in the alloy's microstructure induced an increase in hardness of about 16% and resulted in the reduction of the average scratch depth in comparison to as-cast state.
Signal optimization for transmission Kikuchi diffraction (TKD) measurements in the scanning electron microscope is investigated by a comparison of different sample holder designs. An optimized design is presented, which uses a metal shield to efficiently trap the electron beam after transmission through the sample. For comparison, a second holder configuration allows a significant number of the transmitted electrons to scatter back from the surface of the sample holder onto the diffraction camera screen. It is shown that the secondary interaction with the sample holder leads to a significant increase in the background level, as well as to additional noise in the final Kikuchi diffraction signal. The clean TKD signal of the optimized holder design with reduced background scattering makes it possible to use small signal changes in the range of 2% of the camera full dynamic range. As is shown by an analysis of the power spectrum, the signal-to-noise ratio in the processed Kikuchi diffraction patterns is improved by an order of magnitude. As a result, the optimized design allows an increase in pattern signal to noise ratio which may lead to increase in measurement speed and indexing reliability.
Purpose: The main purpose of the hereby study was the description of microstructure and properties of the new low-carbon Mn-Cr-Mo-V-Ni bainitic cast steel developed in the AGH Laboratory of Phase Transformations for cast mono-blocks of scissors crossovers. Investigations comprise material in as-cast state and after various variants of normalization as well as normalization and high tempering. Design/methodology/approach: Analyses of microstructure, strength properties, impact toughness and crack resistance (KIc) were performed both for material in the as-cast state and after heat treatments. The influence of the initial microstructure on the investigated cast steel hardness – after the normalizing and after the normalizing and tempering – was determined. Findings: Changes in the microstructure of the cast bainitic scissors crossovers were determined and their properties described. Research limitations/implications: The investigations were performed in order to estimate a possibility of applying bainitic cast steels for production of scissors crossovers in the form of monolithic blocks. Practical implications: Application of bainitic cast steels for scissors crossovers in the form of monolithic
In this study, a new biodegradable alloy from the Zn-Ag-Zr system was investigated. Most importantly, mechanical properties and ductility were significantly improved in designed Zn1Ag0.05Zr alloy in comparison to binary Zn1Ag and previously investigated Zn0.05Zr alloys (wt%). The characterized alloy reached values of yield strength, ultimate tensile strength and elongation to failure equal to 166 ± 2 MPa, 211 ± 1 MPa and 35 ± 1%, respectively. Simultaneous addition of both alloying elements contributed to solid solution strengthening, intermetallic Zr-rich phase formation, and effective grain refinement. Immersion and electrochemical in vitro corrosion tests showed a slight increase of degradation rate in ternary alloy up to 17.1 ± 1.0 μm/year and no significant loss of mechanical properties after 28-day of immersion in simulated physiological solution. In addition, the preliminary antimicrobial studies show antimicrobial activity of the investigated Zn-Ag-Zr alloy against Escherichia coli and Staphylococcus aureus. The presented results demonstrate that newly developed Zn-based alloy can be considered as a promising biodegradable material for medical applications.
