Microstructural Characterization of Borided Co-Cr-Mo Alloy

This study involves the effect of boriding powder composition on the microstructure and hardness of a CoCrMo alloy borided in a solid medium using the powder pack method. To investigate the effect of boriding powder composition, two different commercial boriding agents, Ekabor-HM and Ekabor III, were thoroughly mixed with ferrosilicon powders to form the boriding media. The CoCrMo samples were tightly packed with the Ekabor-HM and Ekabor III boriding powders in stainless steel containers to minimize oxidation. The boriding process was carried out under atmospheric conditions for 9 h in an electrical resistance furnace preheated to 1223 K. X-ray diffraction (XRD) analyses revealed that the surfaces of the borided CoCrMo alloys consisted of a bilayer composed of CoB and Co2B phases and also contained minor amounts of CrB, Mo2B5, and Mo2B. The average thickness of the boride layer in the samples borided with Ekabor HM and Ekabor III powders was 28±4.1 μm and 21±2.3 μm, while the average hardness of the boride layer was 1752±5.3 HV0.1 and 1364±3.8 HV0.1, respectively.

Features of the Structure Formation of Diffusion Boride Layers upon Preliminary Activation

The features of the structure formation of diffusion layers obtained by technology, including preliminary surface treatment of steel products made of U8 steel and subsequent boriding in powder media, have been investigated. The pretreatment consisted of dynamic alloying in the superdeep penetration (SDP) mode with a SiC-based powder composition. As a result, the thickness of the diffusion layer increases, its porosity decreases, and the proportion of the high-boron FeB phase in the layer increases.

A study of Thermal Decomposition and Kinetic Evaluation of Boron blended Flash Powder Composition

Herein, the thermal characteristics of flash powders of different combinations of Potassium Nitrate, Sulphur, Aluminium and Boron are reported. From the literature, it is identified that Boron implements lack of sensitiveness to flash powder mixture, which promotes the safety during the manufacturing process. But the thermal behaviour of the Boron blended compositions remain a mystery. Hence, various combinations of flash powder compositions are prepared by keeping the % of KNO3 and % of S as constant, and gradually 23% of Aluminium is reduced (23% to 0) by increasing the quantity of Boron (0 to 23%) in 19 trials, and are subjected to TGA/DSC analysis individually. The TGA and the DSC analysis reveals that the 65.65% replacement of Aluminium with Boron mixture shows predominant characteristics which is suitable for fireworks. Also, the reaction kinetics and the critical ignition temperature are calculated for the optimum composition. The performance of the fireworks product is checked with varying quantity to meet out the optimum quality.

MODE INFLUENCE OF SELECTIVE LASER IMPACT UPON POROSITY OF SAMPLES OF COBALT, CHROMIUM AND MOLYBDENUM POWDERS

The purpose of this investigation consists in the analysis of possibility to obtain products by means of the SLP method using powders of cobalt, chromium and molybdenum having considerable difference in melting temperatures of cobalt (1768ºC), chromium (2130ºC) and molybdenum (2890ºC), density, thermal conduction and solving for the optimum technological modes of powder composition melting to obtain samples with lower porosity. The investigation methods include methods of physical material science. Investigation results and novelty: a procedure for obtaining a powder composite of the cobalt-chromium-molybdenum system for selective laser melting is developed. There are carried out experimental investigations on the selection of optimum technological modes for the layer-by-layer laser melting of a cobalt-chromium-molybdenum alloy of powder composition. A method for layer-by-layer laser synthesis for the solution of a principle matter – possibility for the synthesis of the products of cobalt chromium and molybdenum powders having a considerable difference in melting temperatures, density, heat conductivity and so on. The investigations of model alloy samples of cobalt-chromuim-molybdenum system obtained through the method of layer-by-layer laser synthesis on optimized technological modes through the methods of scanning electronic microscopy allow defining sample porosity. The generalization of obtained numerical and experimental investigation results and definition of essential conditions for selective laser melting allow optimizing modes and parameters of the synthesis. Conclusions: the optimum modes of selective laser melting for obtaining the samples with the powder composition of 66 mas. % Co, 28 mas. % Cr, 6 mas.% Mo through the method of selective laser melting with minimum porosity are: laser capacity P=100Wt, scanning rate v=350mm/s, modulation 5000Hz, scanning pitch s=0.1mm, layer thickness h=0.03mm, melting process takes place in protective argon environment.

Consumer Acceptance on Chocolate Drink Made with a Mixture of Commercial Cocoa Powder and Unfermented Cocoa Powder

Cocoa is one of the foods that contains polyphenol-rich compounds that act as antioxidants. The processing of cocoa into chocolate products generallycauses a decrease in the number of polyphenols. In the development of chocolate beverage products, it is necessary to evaluate sensory evaluation. The purposeof this study was to determine consumer acceptance, total phenolic content (TPC) and antioxidant activity of chocolate drinks made from commercial cocoa powderadded with unfermented cocoa powder. Seventy-five panellist (17-23 years old) contributed to the consumer acceptance of four samples of chocolate drinks witha ratio of commercial cocoa powder: unfermented cocoa powder = 100%:0%, 90%:10%, 80%:20%, 70%:30%. The sample than was analyzed for its antioxidantactivity using the ascorbic acid equivalent antioxidant capacity and total phenolic content using the Folin-Ciocalteau method. The results showed that the sample witha composition of 100% commercial fermented cocoa had the highest value on each sensory attribute. It had the highest TPC (321.235 mg gallic acid equivalent),antioxidant activity (982 ppm), and inhibition percentage (46%), respectively. Addition of the unfermented cocoa powder composition showed a decrease in the level ofconsumer preference. However, the addition did not significantly affect the total phenolic content, but slightly increased the antioxidant activity. The use of unfermentedcocoa powder for mixing components that are not processed standardly has not been well received by consumers, proper processing of unfermented cocoa powderis required if the polyphenol compound is desired.

The Effect of Powder Composition on the Microstructure and Corrosion Resistance of Laser Cladding 60NiTi Alloy Coatings on SS 316L

Two kinds of 60NiTi powders were prepared by pure Ni mixed with Ti powders, and 55NiTi alloy powder with pure Ni powder and both the powders were fully mixed by alcohol ball milling. Two kinds of coatings (denoted as 60Ni-40Ti and 55NiTi-5Ni) were prepared on a 316L stainless steel substrate by laser cladding. The microstructure, microhardness and electrochemical behavior of the prepared coatings were investigated extensively. The results show that 55NiTi-5Ni has a typical dendritic eutectic structure, but 60Ni-40Ti tends to form a eutectic network structure. The main phases in both coatings are (Ni, Fe)Ti and (Ni, Fe)3Ti; however, the (Ni, Fe)Ti phase is dominant in 55NiTi-5Ni, but the (Ni, Fe)3Ti phase is more prevalent in 60Ni-40Ti. The microhardness was significantly improved with the 316L stainless steel substrate, and the microhardness of 55NiTi-5Ni is slightly higher than 60Ni-40Ti. The corrosion resistance of the two coatings in 3.5 wt% NaCl solution also leads to significant improvements compared with the substrate, and the corrosion resistance of 55NiTi-5Ni was also increased. These different behaviors and characteristics might be related to the different microstructures. Uniform and fine eutectic structure in 55NiTi-5Ni coating lead to better performance, which is also conducive to the formation of the dense oxide film to improve corrosion resistance.

Activation of diffusion during the formation of boride layers on the surface of steel parts

The features of structure formation of diffusion layers obtained by the technology, including preliminary surface treatment of steel products and subsequent thermal diffusion boriding in powder media, have been investigated. Pretreatment consisted in surface activation by superdeep penetration with a powder composition based on SiC of steel samples made of У8 steel. The features of the activation zones and their distribution over the surface are noted. The features of the activation zones and their quantitative characteristics are noted. A structural analysis of the obtained diffusion layers for the variants of low-temperature (650 °C) and high-temperature (920 °C) boration has been carried out. The chemical composition of the layer and the distribution of the main elements in it are analyzed. In both cases, a change in morphology was noted, consisting in the formation of a more compact diffusion layer and rounding of boride needles in the zone adjacent to the base metal. An increase in the layer thickness by 20–50 % and an increase in the proportion of the high-boron FeB phase relative to the variant of borating without preliminary activation were established.

Influence of Mechanical Activation and Mechanical Alloying on the Structure, Phase State of the Fe-Ni-Co-Al-Nb Powder Composition and on High-Entropy Coatings Based on it

The article presents the assessment study of mechanical activation and mechanical alloying effect on the structure, phase state of the powder composition and of the coating based on it. The duration of mechanical activation was varied as follows: 1 h, 2 h, 4 h, 8 h, 16 h, 32 h. It is shown that in order to from a high-entropy FeNiCoAlNb alloy on the workpiece surface the duration of mechanical activation must be at least 4 hours. We described the mechanism of mechanical alloying and ways of accelerating this process.