Infiltration is an extensively used technique in the production of Diamond Impregnated Bits (DIBs) commonly used for drilling in both mineral exploration and the Oil&Gas industry. This paper describes research into liquid phase sintering (LPS) as an alternative to commonly used infiltration processes. The great wear resistance and high cutting ability necessary for these tools in turn requires a high diamond concentration and a large volume fraction of wear-resistant components, such as tungsten carbide and/or eutectic tungsten carbide particles. With relatively large particles that do not contribute to densification, the LPS system researched was designed with a relatively large amount of permanent liquid phase sintering, with, rearrangement being selected as the primary densification mechanism owing to the stability of the hard phases. After testing various binder phases and evaluating the influence of the liquid phase volume fraction and presence of some sintering aids, results are promising. Bonds with better sintering behaviour were characterized, while hardness, microstructure, abrasive wear resistance, and interaction with diamonds were studied. The proposed 35NiP25Cu40WC bond processed by LPS attained hardness of 66 HRA and wear coefficient of 20 mm3/MPa, levels similar to those obtained by hot pressed components currently used in the diamond drilling tool industry (19 mm3/MPa).

The sinterability of a commercial Fe-Cu pre-alloyed powder, designed to be used as a metallic bond in diamond impregnated tools, has been greatly analyzed by combining dilatometry, computational thermodynamic calculations, and microstructural analysis. The effect of sintering temperature and alloying elements such as graphite and iron phosphide have been taken into consideration in order to demonstrate the capability of tailoring final properties through different strategies, and dilatometry and microstructural analysis have been used to understand the densification process of the alloys. Solid phase sintering was the mechanism taking place during thermal cycle. In fact, a liquid phase appears but because of the high densification level at that time mechanisms associated with LPS do not contribute to densification. Discussion about me-chanical properties has been related to key microstructural phenomena, i.e., grain growth, phase transformation, precipitation, and solid solution. Obtained hardness ranged from 83 HRB to 106 HRB with yield stresses between 450 MPa and 700 MPa and elongations above 3%, while final tensile properties similar to those obtained by cobalt-based powders processed by hot pressing were also obtained.

This study investigated the synthesis of Ag-SnO2-ZnO by powder metallurgy methods and their subsequent electrical contact behavior. The pieces of Lambda g-SnO2-ZnO were prepared by ball milling and hot pressing. The arc erosion behavior of the material was evaluated using homemade equipment. The microstructure and phase evolution of the materials were investigated through X-ray diffraction, energy-dispersive spectroscopy and scanning electron microscopy. The results showed that, although the mass loss of the Ag-SnO2-ZnO composite (9.08 mg) during the electrical contact test was higher than that of the commercial Ag-CdO (1.42 mg), its electrical conductivity remained constant (26.9 +/- 1.5% IACS). This fact would be related to the reaction of Zn2SnO4's formation on the material's surface via electric arc. This reaction would play an important role in controlling the surface segregation and subsequent loss of electrical conductivity of this type of composite, thus enabling the development of a new electrical contact material to replace the non-environmentally friendly Ag-CdO composite.

Hot Isostatic Pressing (HIP) is a well-known technique that lately is gaining more interest because of its growing involvement in the Additive and Near-Net Shape manufacturing fields. When HIP is used for near net-shape manufacturing, the raw gas atomized powders assume the uttermost importance, and special attention should be given to their quality and characteristics. Based on this statement, the powder should be sieved directly after production to select only those that best suit the HIP process. Typically, a broad Particle Size Distribution is indicated for HIP purposes and looks economically advisable because it leads to a higher yield. Despite this, if the PSD is not strictly controlled, particles with high Oxygen content or chemical inhomogeneity could enter the production chain, leading to compacted components with insufficient mechanical properties. In this paper, Nickel-based superalloy Astroloy particles were assessed in depth both at their surface and in the core, dividing them into sub-batches via mechanical sieving. This procedure evidenced which contribution was brought to the final raw material by each sub-batch. Furthermore, physical properties such as flowability and tap density were studied as a function of the PSD. Next, a complete morphological assessment was conducted to understand the possible defects of each sub-batch better. Similarly, every particle group was chemically studied to determine the Oxygen, Carbon, Nitrogen, and Hydrogen content of each sub-batch. Micro and nano indentations combined with EBSD were used to understand how the particle size may affect the mechanical properties of the powders during the Hot Isostatic pressing. Furthermore, EDS and XRD analysis were used to thoroughly understand how Ti segregation starts forming and what effects are likely to develop. Based on these investigations, it was possible to rationally identify the upper and lower boundary for particle PSD without excessively limiting the overall process yield. (c) 2021 Elsevier B.V. All rights reserved.

Astroloy is a Ni-based superalloy with high-volume fraction of gamma ', which gives high temperature properties but reduces its forgeability. Therefore, powder metallurgy manufacturing processes such as Near Net Shape HIPping are the most suitable manufacturing technology for Astroloy. However, NNSHIP has its own drawbacks, such as the formation of prior particle boundaries (PPBs), which usually tend to decrease material mechanical properties. The detrimental effect of PPBs can be reduced by optimizing the entire HIP processing route. Conventional HIP cycles have very low cooling rates, especially in big components from industry, and thus a series of post-heat treatments must be applied in order to achieve desirable microstructures and improve the mechanical properties. Standard heat treatments for Astroloy are long and tedious with several steps of solutioning, stabilization and precipitation. In this work, two main studies have been performed. First, the effect of the cooling rate after the solutioning treatment, which is driven by the materials' thermal mass, on the Astroloy microstructure and mechanical properties was studied. Experimental analyses and simulation techniques have been used in the present work and it has been found that higher cooling rates after solutioning increase the density of tertiary gamma ' precipitates by 85%, and their size decreases by 22%, which leads to an increase in hardness from 356 to 372 HB30. This hardness difference tends to reduce after subsequent standard heat treatment (HT) that homogenizes the microstructure. The second study shows the effect of different heat treatments on the microstructure and hardness of samples with two different thermal masses (can and cube). More than double the density of gamma ' precipitates was found in small cubes in comparison with cans with a higher thermal mass. Therefore, the hardness in cubes is between 4 and 20 HB 30 higher than in large cans, depending on the applied HT.

Precipitation hardened CuCrZr alloy is the baseline option as heat sink material for the water cooled W divertor concept of DEMO owing to its combination of high thermal conductivity and strength. However, traditional processing of CuCrZr by casting and forging or hot rolling involves several challenges: coarsening of Cr precipitates, microstructures highly heterogeneous, or difficulties in obtaining complex geometries. Additive Manufacturing (AM) enables creating innovative solutions with complex structures for heat exchangers and heat sinks. Compared to Laser Powder Bed Fusion (L-PBF), the EB-PBF (Electron Beam Powder Bed Fusion) AM technology offers advantages when processing copper alloys: it avoids difficulties associated to the high thermal conductivity and reflectivity of copper-based materials and prevents their oxidation by working under high vacuum. In this work the study of AM of a CuCrZr alloy with nominal composition 0.6?0.9 Cr, 0.07?0.15 Zr (wt.%) has been performed by EB-PBF. A detailed process parameters study has been performed to identify the process window and obtain dense materials free of defects. The process parameters, including post-built heat treatments like age hardening, were correlated with the microstructural evolution, the thermal conductivity and the hardness. ? 2021 The Authors. Published by Elsevier B.V. All rights reserved. Precipitation hardened CuCrZr alloy is the baseline option as heat sink material for the water cooled W divertor concept of DEMO owing to its combination of high thermal conductivity and strength. However, traditional processing of CuCrZr by casting and forging or hot rolling involves several challenges: coarsening of Cr precipitates, microstructures highly heterogeneous, or difficulties in obtaining complex geometries. Additive Manufacturing (AM) enables creating innovative solutions with complex structures for heat exchangers and heat sinks. Compared to Laser Powder Bed Fusion (L-PBF), the EB-PBF (Electron Beam Powder Bed Fusion) AM technology offers advantages when processing copper alloys: it avoids difficulties associated to the high thermal conductivity and reflectivity of copper-based materials and prevents their oxidation by working under high vacuum. In this work the study of AM of a CuCrZr alloy with nominal composition 0.6?0.9 Cr, 0.07?0.15 Zr (wt.%) has been performed by EB-PBF. A detailed process parameters study has been performed to identify the process window and obtain dense materials free of defects. The process parameters, including post-built heat treatments like age hardening, were correlated with the microstructural evolution, the thermal conductivity and the hardness.

Different approaches to take advantage of powder metallurgy in the manufacturing of diamond-impregnated components were studied. Three different powders were used as starting materials; two pre-alloyed powders, based on Fe-Cu and Fe-Cu-Sn systems, and one pre-mixed Fe-based powder. Different manufacturing routes as a strategy to obtain tailored mechanical properties were studied, with the influence of alloying elements such as graphite, iron phosphide and Mn-Ni-B master alloy to reinforce the iron-based powders. Both uncoated and coated commercial synthetic diamonds were introduced in the systems to analyse the surface reactions that depend on both metallic matrix and processing parameters. Hardness values from 88 to 105 HRB were obtained with a wide range of transverse rupture strength values from 1250 to 1640 MPa. An appropriate combination of metallic matrix, alloying elements and processing parameters makes the materials analysed here suitable powders for the manufacturing of diamond-impregnated tools.

Nanocrystalline Ni (Ni-nc) obtained by mechanical milling may present improved mechanical properties paired with high abrasion resistance. Different sintering processes were used to consolidate Nanocrystaline Ni: hot pressed (HP) and hot-isostatic pressed (HIP). The microstructure, mechanical properties, and tribological were evaluated to compare the processes. X-ray diffraction patterns showed that HIP-consolidated specimens had larger crystallite sizes and 37% less microstrain when compared to the HP specimens. The nanohardness of the HIP specimens was also carried out and it was 50% lower than that of HP specimens, whereas its coefficient of friction found was 25% higher. These results show the advantages of the HP process over the HIP since the high pressure. The low sintering temperature of HP inhibited the grain growth, which leads excellent mechanical and tribological properties of Ni.

Compared to pure tungsten, self-passivating tungsten based alloys for the first wall armor of future fusion reactors shall provide a major safety advantage in case of a loss-of-coolant accident with simultaneous air ingress, due to the formation of a stable protective scale at high temperatures in presence of oxygen preventing the formation of volatile and radioactive WO3. Recently developed W-Cr-Y alloys produced by mechanical alloying and hot isostatic pressing (HIP) exhibit a strong reduction of oxidation rate compared to pure W and high mechanical strength. A heat treatment after HIP at 1555°C results in a one-phase material with a high thermal shock resistance. Nevertheless, the microstructure is metastable and its thermal stability under operational conditions has to be assessed. In this work results of thermal stability tests on heat treated W-10Cr-0.5Y alloy subjected to temperatures of 650, 700, 800 and 1000°C for times ranging from 50 to 1000h are presented. After 1000h at 650°C and 100h at 700°C no visible change of the microstructure is detected. After 100h at 1000°C a complete decomposition takes place with the formation of a uniform, fine-scale mixture of W- and Cr-rich phases, typical for spinodal decomposition.

Once the feasibility of the STARS route (Surface Treatment of gas Atomized powder followed by Reactive Synthesis) has been demonstrated to produce ODS ferritic steels by internal oxidation avoiding mechanical alloying, two strategies are proposed in this work to enhance precipitation of oxide nanopArtículos. Firstly, consolidation by Spark Plasma Sintering (SPS) is used to produce finer microstructures compared to HIP consolidation. SPS parameters like temperature, heating rate, pressure and time of exposure under pressure were explored, and dense samples (up to 99,5%RD) were obtained. Secondly, precipitation of nanopArtículos is achieved through a combination of HIP consolidation at low temperature (700-900 degrees C) followed by hot deformation under the presence of metastable oxides, to increase the density of dislocations, preferential nucleation sites for the precipitation of nanometric Y-Ti-O oxides. Deformation dilatometry and plane strain compression tests were performed to simulate hot deformation under different hot rolling schedules. Total deformation, number of passes, time between passes or initial and final rolling temperatures are some of the parameters explored. Microstructural characterization by Scanning Electron Microscopy (SEM) of consolidated materials is presented.