Erosion-corrosion of Cr3C2-Ni cermets in salt water

Chromium carbide based cermets are popular materials in different industrial applications due to their unique properties. These materials have outstanding erosion resistance up to 1000 °C and excellent oxidation resistance up to 850 °C. Their corrosion resistance in different corroding mediums is favorably higher than that of conventional WC hard metals or stainless steel. These materials can be applied as coatings with properties comparable to bulk materials. In this work different regimes with prevailing role of erosion or corrosion processes were found. Erosion-corrosion maps for material selection were constructed and discussed. The weight loss of the samples during simultaneous effect of corrosion and wear processes was found to be complicated and cannot be evaluated as simple summation of these two processes. SEM study of material surfaces before and after erosion-corrosion tests were conducted and the prevailing mechanisms of the material behaviour were evaluated

High Temperature Sliding Wear of NiAl-based Coatings Reinforced by Borides

The development of composite materials (CM) in the systems "metal-refractory compound" is one of the up-to-date trends in design of novel materials aimed at operating under the conditions of significant loads at high temperature. To design such material, NiAl, which is widely used for deposition of protective coatings on parts of gas-turbine engines, was selected for a matrix. To strengthen a NiAl under the conditions of intense wear and a broad temperature range (up to 1000 °C), it is reasonable to add refractory inclusions. Introduction of refractory borides into matrix leads to a marked increase in metal wear resistance. In order to research the behavior of the designed composites at high temperatures and to study the influence of oxides on the friction processes, the authors carried out high temperature oxidation of CM of the above systems at 1000 °С for 90 min. It was determined that all of the composites were oxidized selectively and that the thickness of oxide layers formed on the boride inclusions is 3 – 7 times that on the oxides formed on the NiAl matrix. The mechanism of wear of gas-thermal coatings of the NiAl – МеB2 systems was studied for conditions of high temperature tribotests using the «pin-on-disc» technique. The obtained results indicate that introduction of TiB2, CrB2 and ZrB2 leads to their more intense oxidation during high temperature tribotests as compared to the matrix. The oxides formed on refractory borides act as solid lubricants, which promote a decrease in wear of the contact friction pairs. For more detailed investigation of the effect of tribo-oxidation products on the friction processes, tribotests were conducted for prior oxidized (at 900 °С) coatings NiAl – 15 wt.% CrB2 (TiB2, ZrB2)

Metal coating of ceramic microspheres: A new precursor for realising metal-based syntactic foams

Coating of cenospheres (CS) with thin layers of metal – namely Cu and stainless steel 316 (Me@CS) - by means of vibration-assisted Physical Vapor Deposition (PVD), particularly by magnetron sputtering, yields a starting material with considerable potential for production of new types of metal matrix syntactic foams (SF) as well as optimized variants of conventional materials of this kind. The present study introduces the coating process and the production of samples via spark plasma sintering (SPS). The influence of processing parameters on the coating itself and the syntactic foams obtained are discussed in terms of density levels as a function of sintering temperature and surface appearance before and after sintering. Cylindrical samples are subjected to conductivity measurements and mechanical tests and first performance characteristics are reported. The observed compressive strengths for Cu-based materials in a density range of 0.87-1.28 g/cm3 is found to lie between 8 and 30 MPa, depending on sintering conditions. For the 316 steel based materials in a density range of 1.10-1.90 g/cm3 the compressive strengths is found to lie between 35 and 55 MPa, depending on sintering conditions. In this study, as hollow ceramic microspheres, cenospheres with a chemical composition of 53.8±0.5 wt.-% SiO2, 40.7±0.7 wt.-% Al2O3, 1.4±0.2 wt.-% CaO and 1.0±0.2 wt.-% Fe2O3, plus smaller amounts (below 1 wt.-%) of MgO, Na2O and K2O were used. Please click Additional Files below to see the full abstract

Optimisation of trabecular bone mimicking silicon-hydroxyapatite based composite scaffolds processed through selective laser melting

Additive manufacturing is a rapid prototyping technology to produce complex three-dimensional scaffolds suitable for personalized medicine. In the present study, the laser powder bed fusion through a selective laser melting (SLM) approach has been applied to optimized fabrication of bio-mimicking scaffolds by using hydroxyapatite (HAp, 50 and 70 wt%) and silicon powder mixture. In situ formation of pseudo-wollastonite (P–W, CaSiO3) has been detected along with silicon for 50 wt% of HAp powder mixture, while an increase in HAp content has resulted in P–W, silicon and larnite (Ca2SiO4) formation. The pore size of 400 μm, according to the CAD model, are observed at the scaffolds fabricated at the shortest exposure time (50 μs), lowest laser current (500 mA) and energy density (41.6 J/mm3), and simultaneously at the highest scanning speed. Compressive stress demonstrated by the fabricated scaffolds is shown to be acceptable for their use in metaphyseal region of long bones.</p

Macroporous silicon-wollastonite scaffold with Sr/Se/Zn/Mg-substituted hydroxyapatite/chitosan hydrogel

The scaffolds, which morphologically and physiologically mimic natural features of the bone, are of a high demand for regenerative medicine. To address this challenge, bioactive porous silicon/wollastonite (SC) scaffold has been developed for potential bone tissue engineering applications. Additive manufacturing through the selective laser melting approach has been exploited to fabricate computer-aided designed scaffolds with a pore size of 400 μm. To increase the biocompatibility and osteogenic properties of SC scaffolds, the hydrogel based on a mixture of four mono-substituted hydroxyapatites (sHAp) and biopolymer chitosan (CHT) has been incorporated into SC by impregnation and freeze-gelation method. The pore size of 400 μm of SC has provided enough space for the impregnation of polymer solution and composite (CHT/sHAp) suspension to form highly porous hydrogel within pores. By the combination of SC and CHT/sHAp, both cell attachment and homogeneous proliferation on SC scaffold as well as mechanical properties of CHT/sHAp hydrogel have been improved.</p

Laser Powder-Bed Fusion of Ceramic Particulate Reinforced Aluminum Alloys: A Review

Aluminum (Al) and its alloys are the second most used materials spanning industrial applications in automotive, aircraft and aerospace industries. To comply with the industrial demand for high-performance aluminum alloys with superb mechanical properties, one promising approach is reinforcement with ceramic particulates. Laser powder-bed fusion (LPBF) of Al alloy powders provides vast freedom in design and allows fabrication of aluminum matrix composites with significant grain refinement and textureless microstructure. This review paper evaluates the trends in in situ and ex situ reinforcement of aluminum alloys by ceramic particulates, while analyzing their effect on the material properties and process parameters. The current research efforts are mainly directed toward additives for grain refinement to improve the mechanical performance of the printed parts. Reinforcing additives has been demonstrated as a promising perspective for the industrialization of Al-based composites produced via laser powder-bed fusion technique. In this review, attention is mainly paid to borides (TiB2, LaB6, CaB6), carbides (TiC, SiC), nitrides (TiN, Si3N4, BN, AlN), hybrid additives and their effect on the densification, grain refinement and mechanical behavior of the LPBF-produced composites

Some views on the erosion-corrosion response of bulk chromium carbide based cermets

Chromium carbide/nickel based composites are applicable in many environments involving tribo-corrosion due to their combined ability to resist wear and corrosion. Hence, they are candidate materials for use either in bulk as surface coatings in crude oil (offshore) or in power and marine industries. The aim of this work was to study the effect of material parameters such as composition and surface roughness, together with test conditions such as abrasive particle concentration, applied potential, temperature and time of experiment on the performance of chromium carbide based cermets. Potentiodynamic and potentiostatic tests were carried out as part of this work. SEM studies were also conducted to establish the mechanisms of the material degradation processes. Finally, erosion-corrosion maps were constructed based on the results. Material wastage, synergy and regime maps were developed for these materials and demonstrated that the performance of the cermet depends on the interplay of material and process variables

Bioactive Ceramic Scaffolds for Bone Tissue Engineering by Powder Bed Selective Laser Processing: A Review

The implementation of a powder bed selective laser processing (PBSLP) technique for bioactive ceramics, including selective laser sintering and melting (SLM/SLS), a laser powder bed fusion (L-PBF) approach is far more challenging when compared to its metallic and polymeric counterparts for the fabrication of biomedical materials. Direct PBSLP can offer binder-free fabrication of bioactive scaffolds without involving postprocessing techniques. This review explicitly focuses on the PBSLP technique for bioactive ceramics and encompasses a detailed overview of the PBSLP process and the general requirements and properties of the bioactive scaffolds for bone tissue growth. The bioactive ceramics enclosing calcium phosphate (CaP) and calcium silicates (CS) and their respective composite scaffolds processed through PBSLP are also extensively discussed. This review paper also categorizes the bone regeneration strategies of the bioactive scaffolds processed through PBSLP with the various modes of functionalization through the incorporation of drugs, stem cells, and growth factors to ameliorate critical-sized bone defects based on the fracture site length for personalized medicine

Interaction between particle erosion, aqueous corrosion and binder content in chromium carbide based cermets at room temperatures

Paper examining the interaction between particle erosion, aqueous corrosion and binder content in chromium carbide based cermets at room temperatures

SHS-Derived Powders by Reactions’ Coupling as Primary Products for Subsequent Consolidation

The capability of self-propagating high-temperature synthesis (SHS) to produce powders that are characterized by a high sintering ability, owing to high heating and cooling rates inherent to the exothermic reaction, is of a special interest for the industry. In particular, SHS-derived powders comprise a significant defect concentration in order to effectively enhance the mass transfer processes during the sintering, which allows for the successful consolidation of difficult-to-sinter materials at relatively low sintering temperatures. From this perspective, the design of precursors suitable for sintering, synthesis in a controlled temperature regime and the optimization of geometrical and structural parameters of SHS powders as a potential feedstock for the consolidation is of key importance. Here, we report on the comparative studies concerning the SHS processing of composites for advanced powder metallurgy techniques. The synthesis and sintering peculiarities of the SHS through coupled reactions in the Me’O3(WO3,MoO3)-Me’’O(CuO,NiO)-Mg-C, Ti-B-Al12Mg17 systems are comparatively reviewed. The SHS coupling approach was used for the preparation of powders with a tuned degree of fineness (a high specific surface area of particles), a high-homogeneity and a controllable distribution of elements via both the regulation of the thermal regime of combustion in a wide range and the matching of the thermal and kinetic requirements of two interconnected reactions. Microstructural features of the powder feedstock greatly contributed to the subsequent consolidation process