The accurate determination of the total hemispherical emission coefficient (THEC) of materials is essential for modelling radiative heat transfer in high-temperature vacuum environments. This study presents a rapid steadystate calorimetric method to determine the THEC using a vacuum electron beam (EB) facility. A graphite-coated Inconel 718 foil with a thickness comparable to the electron penetration depth was used as the emission target, allowing temperature equalization within seconds. Surface temperatures were recorded via a calibrated twocolour thermal imaging system. An in-situ calibration was conducted, using the melting point of pure copper as a fixed reference. Numerical simulations were employed to validate both the emissivity determination and the temperature calibration methodology. EB heating efficiency was determined at 150 keV in a combined experimental-simulative approach using Monte Carlo simulations and backscattered electron intensity capture. Temperature calibration showed high reproducibility with a median absolute deviation of +/- 0.4% and a half range of +/- 1.1 % at 1085 degrees C, and was shown to be transferable to other materials. EB heating efficiency slightly decreased from 0.832 +/- 0.003 at room temperature to 0.825 +/- 0.002 between 800 degrees C to 1140 degrees C. THEC values between 0.88 and 0.92 with a maximum half range of +/- 0.06 were obtained in the range of 840 degrees C to 1110 degrees C for graphite-coated Inconel 718 with a median roughness of Ra = 1.2 mu m. Reflected radiation from the emission target and thermal losses from conduction and sublimation were assessed and found negligible. Results were consistent with literature, particularly under high surface roughness or pre-oxidized conditions.

In this study, a mechanically alloyed equiatomic AlCuCrFeNi high-entropy alloy (HEA) was used as the starting point for a thermodynamically guided alloy design aimed to promote the formation of an FCC solid-solution microstructure. Two modified alloy compositions were developed by adjusting the elemental ratios to enhance phase stability based on thermodynamic parameters such as mixing enthalpy, configurational entropy, atomic-size mismatch, and valence electron concentration. The alloys were synthesized using mechanical alloying (MA), followed by the Field Assisted Sintering Technique/Spark Plasma Sintering (FAST/SPS) to obtain a fine-grained microstructure. The experimental results revealed that a multiphase microstructure was obtained, which consists of an FCC matrix, a secondary FCC phase, carbides, and intermetallic compounds, indicating that a single-phase FCC solid solution was only partially stabilized under the applied processing conditions. Mechanical testing showed high compressive strengths of 1893 MPa and 1882 MPa, respectively, combined with limited plasticity at room temperature. When tested at 300 degrees C, the compressive strength decreased by approximately 20 %, while ductility was significantly enhanced. Fractographic analysis revealed a shear-type fracture, showing brittle, carbide-induced crack initiation at room temperature and a transition to more ductile fracture behavior at elevated temperatures. Both alloys exhibited high Vickers macrohardness values ranging from 522 to 552 HV10 at room temperature, surpassing that of conventional Ti-6Al-4 V. Furthermore, the contributions of grain refinement and solid-solution hardening to the measured macrohardness were theoretically estimated, revealing that solid-solution hardening is the dominant strengthening mechanism.

Within the scope of this study, the macroscopic temperature distribution in the steady-state temperature condition during Field Assisted Sintering Technique/Spark Plasma Sintering (FAST/SPS) in functionally graded materials (FGM) was investigated. The sample material exhibited a diameter of 50 mm and a thickness of 9 mm. The FGM samples were composed of steel X2CrMnNi 16-7-6 and Mg-PSZ ceramic (MgO partly stabilized ZrO2). By varying the sintering tool setup, a specific modification of the macroscopic temperature distribution within the sample material and the sintering tool was achieved. The aim of the modifications was to optimize the temperature gradients in order to allow for the simultaneous compaction of all FGM layers under ideal circumstances. This involves achieving enhanced ceramic densification without inducing steel melting. Finite element method (FEM) simulations were carried out to get information about the temperature distribution within the sample material and the sintering tool. Furthermore, for this propose, thermocouple temperature measurements were conducted at various measurement points on pre-sintered FGM within the specific sintering tool setup. Additionally, all findings regarding the temperature distribution within the sample material and the sintering tool were compared with results concerning the temperature distribution from the microstructural and mechanical characterization of the center and edge regions of the FGM samples. The FGM samples exhibited a significant increase in temperature from the center to the edge in the radial direction depending on the used sintering tool setup. While the FGM samples showed only minor vertical temperature gradients in the center, the highest vertical temperature gradients were determined at the edge of the FGM sample using an asymmetric sintering tool setup.

The solidification behavior of a novel X1CrCuNiN 18-9-6 (concentrations in wt%) stainless steel is studied by thermodynamic calculations and corresponding microstructure investigations. The thermodynamic calculations of the X1CrCuNiN 18-9-6 steel predict a metastable austenitic structure, which is verified by microstructural analyses. In the as-cast state before heat treatment, a few copper precipitates, mostly over 50 mu m in size, are visible, which are located exclusively in the interdendritic regions. The electrode inert gas atomization process is applied to produce a steel powder using a pre-material in as-cast state with significantly increased Cu content of 9 wt%. After atomization, despite the rapid cooling, micrometer-sized copper precipitates form again, which are homogeneously distributed in the microstructure, but are mostly less than 10 mu m in size and thus much finer than in the initial cast state. The short processing times during field-assisted sintering technique/spark plasma sintering makes it possible to produce a bulk material with a porosity of less than 1%. Miniature samples produced from the as-sintered material exhibit uniform elongation values of 30%-40% with a tensile strength of about 640 MPa under tensile loading conditions.

The study evaluates the effect of electrochemical hydrogen charging on the tensile properties and fracture behavior of the plasma tungsten inert gas weld of the high‐alloy austenitic steel X3CrMnNiMoN17‐8‐4 in comparison to the pure base metal (BM). The weld metal exhibits a higher susceptibility to hydrogen embrittlement than the BM, which is mainly expressed by a loss in ductility. Based on the performed electron backscatter diffraction and X‐ray diffraction examinations, this is attributed to the higher amount of δ‐ferrite and the higher dislocation density in the weld zone. Furthermore, fractographic analyses reveal a change in the manner of fracture mode from ductile to brittle fracture starting from the edge in the hydrogen charged samples. The wider area of brittle fracture in the weld seam in relation to the BM indicates that hydrogen penetrates deeper into the material. Consequently, the diffusivity of hydrogen in the weld seam is determined to be significantly higher than in the BM.

This study examines a quenched and partitioned steel matrix composite, which was reinforced with 10 vol% Mg-PSZ and processed by Spark Plasma Sintering (SPS). The investigations focused specifically on the effect of solution annealing prior to Quenching and Partitioning (Q&P) treatment on the microstructure and the mechanical properties under compressive loading of the composite. The results revealed that the solution annealing step is necessary to form alpha '-martensite after quenching during the Q&P treatment, which strengthens the material. Furthermore, a substantial amount of Mg-PSZ was found to have transformed in a stress-induced manner under compressive load if a certain fraction of alpha '-martensite was present in the initial microstructure. However, the solution annealing slightly intensified the destabilization of the Mg-PSZ.

This chapter analyses options to synthesis TRIP matrix composites (reinforced with Mg-PSZ), which stand out due to a high strength and the possibility to undergo a stress- and strain-induced phase transformation. These composites are processed using Field Assisted Sintering Technology (FAST). Both, the influence of the powder treatment before sintering and the impact of parameter setting during sintering by FAST are discussed. Due to a careful alignment of these factors, a TRIP matrix composite (reinforced with 5 vol% Mg-PSZ) with an 1% compressive yield strength of 700 MPa was generated. Furthermore, both composite components exhibited a phase transformation during compressive deformation. The fundamental investigations are the basis for the development of Functionally Graded Materials (FGM) with a varying Mg-PSZ content along the sample height. To synthesize these FGMs by FAST, a temperature gradient has to be generated during sintering, which allows to sinter the pure ceramic layer without melting the steel phase. Several possibilities to generate a temperature gradient are discussed.

High‐alloy Fe–19Cr–3Mn–4Ni–0.5Si–0.17N–0.17C TRIP/TWIP steel samples are processed by SPS/FAST (Spark Plasma Sintering/Field‐Assisted Sintering Technology) and subsequently thermo‐mechanically treated by Quenching‐Deformation‐Partitioning (QDP). Because a martensite start temperature (Ms) does not exist for this material, it is not possible to form as‐quenched α’‐martensite during the QDP treatment. Therefore, α’‐martensite is formed by strain‐induced transformation. To investigate the influence of the compressive deformation step of the QDP treatment (referred to as pre‐deformation) and the combined α’‐martensite formation on the microstructure and the mechanical properties, the deformation temperature is varied between −60 °C and 20 °C for two different strain rates (0.0004 s−1 and 1 s−1). The results show that a reduction in pre‐deformation temperature and a low strain rate increase the volume fraction of strain‐induced α’‐martensite during pre‐deformation. Furthermore, the compressive yield strength increases. It is obvious that the austenitic‐martensitic QDP‐treated steel could be assigned to the 3rd generation of Advanced High Strength Steels (AHSS). The steel exhibits compressive offset yield strengths of between 1400 MPa and 1700 MPa as a function of the QDP conditions and the α’‐martensite content which is formed during pre‐deformation.

Welding of Mg‐PSZ‐reinforced TWIP metal matrix composites (TWIP MMC) requires precise control over the level of dilution: otherwise, the risk of cavity formation arises. For this work, dissimilar joints between a TWIP MMC and an AISI 304 stainless steel are produced by means of electron beam welding over a wide range of process parameters. The influence of the welding process on the dilution, the microstructure of the welding seam, and the mechanical properties is presented and classified according to DIN EN ISO 13919–1. Furthermore, the welding quality of the samples is characterized by non‐destructive testing methods such as the novel uit and X‐ray analysis. It is shown that joints with EG ≥ ‘C’ can be produced with a high degree of reproducibility within a parameter window of Δx = 0.40.6 mm at welding speeds of 15 and 5 mm s −1 . The main defects are cavities, underfill, and lack of fusion which can all be detected by the uit down to a minimum defect size of 90–100 µm. Lower welding speeds and a slight underfocus decrease the tendency toward defects and for a (Δx) = 0.5 mm, tensile properties are achieved to match the level of the TWIP MMC.

Many publications investigate temperature distributions by simulations. Temperature is often not practically measured or only at a few locations inside the sintering tool using thermocouples. However, thermocouple temperature measurement is very sensitive to environmental conditions and can be extremely defective. This study investigates the feasibility of thermocouple temperature measurement at different measuring positions within a graphite tool during SPS/FAST. Three different graphite tool setups and three different thermocouples were used for the temperature measurements. The thermocouples were covered by an Al2O3 tube and placed directly inside a borehole in the setup. Process temperatures, measured by a vertical pyrometer, up to 1200 degrees C were realized. Experimental data at different temperature plateaus show significant temperature differences depending on the applied thermocouple and tool setup. It is shown that the temperature present is underestimated by the thermocouple and measuring errors vary drastically with the thermocouple length, which is inserted in the sintering tool. (C) 2019 Elsevier Ltd. All rights reserved.

In situ TiB and TiC particle-reinforced titanium matrix composites (TMCs) based on a near-β Ti-5Al-5Mo-5V-3Cr alloy (Ti-5553) reacting chemically with B4C were processed by spark plasma sintering (SPS). The influence of powder milling parameters (low-energy mixing or high-energy milling) on the chemical reaction behavior between the matrix and the B4C particles during sintering was investigated. Taking the microstructure into account, characterization of the particle strengthening effect was carried out under compressive loading conditions. High-energy milling resulted in a significantly higher degree of B4C conversion during sintering. This was attributed to plastic deformation of the initial matrix powder and more homogeneous distribution of the B4C particles accompanied by a significant reduction in cluster formation. In comparison to the unreinforced Ti-5553 matrix, the hardness, stiffness, and compressive strength of the TMCs were successfully increased due to particle reinforcement. The powder milling treatment improved these properties further—a phenomenon directly associated with the higher degree of B4C conversion. Instead of the expected formation of stoichiometric TiC, the formation of nonstoichiometric TiC1−x with x ≈ 0.5 was observed. Molybdenum, vanadium, and chromium formed a solid solution in TiB and TiC1−x. Additionally, the titanium content in the matrix particles was markedly reduced, while the aluminum content roughly doubled.

A composite material provides the opportunity to combine the positive properties of two or more different materials. Thus, the composite material exhibits superior properties compared to those of the single components. One example, which is in the focus of research, represents a composite consisting of a TRIPsteel matrix (TRansformation Induced Plasticity) reinforced with Mg-PSZ (partially stabilized zirconia) [1-4]. TRIP-steels exhibit a high strength as well as a high ductility due to a deformation-induced phase transformation from metastable austenite to α’-martensite [5,6]. Furthermore, the Mg-PSZ is able to transform stress-induced from the tetragonal phase into the monoclinic phase. Thus, a volume expansion occurs, which is responsible for an enhanced strength within the composite material [7].

In-situ TiB/TiC particle-reinforced titanium matrix composites (TMCs) based on a near-β Ti-5Al-5Mo-5V-3Cr alloy (Ti-5553) were synthesized by solid-state reaction with B4C and graphite particles during spark plasma sintering (SPS). In this study, investigations were focused on the influence of the molar TiB:TiC ratio on the mechanical properties of the composites. With respect to the adjustment of the molar TiB:TiC ratio, the formation of stoichiometric TiC or nonstoichiometric TiCy was considered as the literature provides conflicting information in this respect. Furthermore, the solid-state reaction behavior influenced by the matrix alloying elements is discussed in comparison to a pure titanium matrix. The hardness, compressive strength and bending strength of the TMCs were improved successfully due to the TiB and TiC particles maintaining acceptable levels of ductility. However, X-ray diffraction experiments revealed that for the adjustment of the molar TiB:TiC ratio, the stoichiometry of the TiCy particles formed must be considered as nonstoichiometric TiC0.5 resulted from the solid-state reaction of carbon and titanium. Compared to TMCs with pure titanium matrices, more sluggish solid-state reaction kinetics were observed. This was attributed to the matrix alloying elements molybdenum, vanadium and chromium, which formed solid solutions within the reinforcing particles.

Two different preparation routes were applied to process WC-MgO composites with varying MgO contents (4.1 wt.% and 5.9 wt.% MgO). WC-MgO powder mixtures were synthesized by a milling process at 600rpm for 6h of partially oxidized WC (WC+WO3), Mg3N2 and C. Alternatively, WC and MgO as initial powders were used. For consolidation of the powder mixtures the field-assisted sintering technology (FAST) was used. X-ray diffraction shows that samples out of different powder mixtures and sintered between 1600°C and 1750°C exhibited WC, MgO and the W2C phase independent of the preparation route of the powder mixtures. A higher density and better mechanical properties (hardness and indentation fracture toughness) of WC-MgO were achieved of pure WC and MgO as initial powders were consolidated by FAST. It was found that a lower MgO content results in higher hardness values and in a slightly decreased indentation fracture toughness.

TiN–AlN powder mixtures of commercial TiN and AlN powders with variable AlN contents (15vol% and 25vol%) were ball-milled for 3 and 6h before subsequent consolidation by spark plasma sintering (SPS). The high-energy ball milling process induced mechanical alloying of the TiN with AlN, which was associated with the incorporation of AlN into the crystal structure of the TiN. In addition to the primary phases, which were the face centered cubic TiN and hexagonal wurtzitic AlN, the sintered samples contained crystalline γ-AlON after sintering. This study investigated the effect of the powder milling time, the sintering temperature and the AlN volume fraction on the hardness, fracture toughness and compressive strength of the TiN–AlN composites. It was found that the sintering temperature (1600°C or 1700°C) had only a marginal influence on the mechanical properties. An increase in hardness and a slightly enhanced average fracture toughness were caused by the increase of the AlN content from 15vol% to 25vol%. An influence of the AlN volume fraction on the compressive strength could not be determined.

The steadily increasing need for energy resources represents a challenge in every aspect. The fossil energy resources are limited and may be locked several thousand meters below the surface, which may also imply the need of highly complex wellbores and results in high costs. In order to be able to reach these resources, special tools and equipment are needed. These tools are exposed to extreme conditions such as high loads, high temperatures and pressures as well as abrasive conditions while in contact with the formation. Under such conditions, the tool and component lifetime also has an economic impact. A current challenge is to extend the lifetime of the tools and components. The materials being used include polycrystalline diamond compact (PDC), thermally stable polycrystalline diamond (TSP) and cemented carbides, i.e. tungsten carbide-cobalt alloys. Tungsten carbide-cobalt alloys are extensively used for several applications such as inserts for roller cone drilling bits, cutting plates and wear protection. For these alloys, the wear resistance is closely related to the hardness, however, an increase in the hardness reduces the fracture toughness of the material. In sintered hard metals processed through the traditional routes, such as Hot Isostatic Pressing (HIP) or Hot Pressing (HP), grain growth inhibitors are often used to accomplish a fine grain size in the order of µm. With the FAST technique (Field Assisted Sintering Technology) it is possible to produce bulk materials in the near-nano range (WC grain size dWC ≈ 200 nm) without the use of grain growth inhibitors. In order to prove the suitability of FAST tungsten carbide alloys in the near-nano range for drilling tools and components, comparative tests between standard materials and FAST material are conducted in a small scale drilling test stand. Tests are performed on different rocks to reproduce different formation types. The results of a test series on granite and sandstone are presented. The preliminary results are promising, since the FAST material exhibits less wear than the standard materials.

Ceramic particle reinforced metal matrix composites (PRMMCs) combine the strength and brittleness of ceramics with the toughness of a metallic matrix. In order to use these materials in construction and operational design their fracture mechanical behavior must be evaluated. In this study, a 30 vol.-% Al2O3 reinforced austenitic TRIP steel processed by powder metallurgical technique was investigated using precracked miniature SENB-specimens in 3-point-bending. An elastic-plastic analysis by means of the J-integral method in combination with optical crack observation showed the materials ability of stable crack growth, i. e. R-curve behavior. In addition to the mechanical tests microstructural studies were performed, whereby particle debonding and fracture as well as martensitic phase transformation and crack bridging within the matrix were identified as fracture energy dissipating mechanisms.

The failure behaviour of WC-Co hard metals with binder contents of 6 and 12 wt.% was investigated under repeated dynamic loadings. The materials were consolidated by field-assisted sintering and exhibited WC grain sizes of about 200 nm. Static and dynamic strength tests on a servo-hydraulic testing machine and a modified split Hopkinson pressure bar (MSHPB), respectively, resulted in compressive fracture strengths between 4370 MPa and 6660 MPa depending on the Co content and the applied strain rate. Moreover, the hard metal samples were repeatedly loaded in the MSHPB below their compressive strength at different stress levels, and subsequently investigated by eddy current testing after each loading step. The measured eddy current signal was dependent on the stress level and the number of impacts. Additionally, the damage of the samples was examined with the help of images from the scanning electron microscope (SEM).Static strength tests of the pre-damaged material revealed that the residual strength of WC-6Co decreases with an increasing number of impacts. In contrast, WC-12Co shows strain hardening caused by the multiple-impact loadings. The size of the fragments revealed intensified microcrack initiation. (C) 2015 Elsevier Ltd. All rights reserved.

The strain-rate dependence of WC-Co hard metals with binder contents of 6, 8, 10 and 12 wt% was investigated. The materials were processed by spark plasma sintering and exhibited WC grain sizes of about 200 nm. Static compressive strength was investigated using a servo-hydraulic testing machine. Dynamic compression tests were performed in an instrumented drop-weight tester as well as a modified Split-Hopkinson pressure bar (MSHPB). The compressive strength of the cylindrical test specimens increased with decreasing Co content and increasing strain rate, from 4370 MPa for WC-12Co under quasi-static loading to 6660 MPa for WC-6Co under dynamic loading.For the evaluation of the fracture mechanisms, the fragment size of the broken parts was determined by optical particle analysis. The results indicated an increase in microcrack density with increasing strain rate.Based on the findings, different model curves were fitted to the experimental data to describe the strain-rate dependent compressive strength with respect to Co content. (C) 2014 Elsevier B.V. All rights reserved.