Frictional and wear behaviour of AlCrN, TiN, TiAlN single-layer coatings, and TiAlN/AlCrN, AlN/TiN nano-multilayer coatings in dry sliding

This paper examines the frictional and wear behaviour of AlCrN, TiN, TiAlN single-layer coatings, and TiAlN/AlCrN, AlN/TiN nano-multilayer coatings in dry sliding. Comparative studies on the coatings sliding in air and vacuum environment at different speeds provided important insight on the effect of oxidation and temperature on the frictional and wear behaviour of the coatings. Among all the single-layer coatings tested in vacuum, TiN gave the lowest coefficient of friction (COF), followed by TiAlN and AlCrN. This indicated that TiN was the most lubricous coating. At 10 m/min in ambient air in which oxidation took place, AlCrN gave the lowest COF, followed by TiN and TiAlN. Among the two types of nano-multilayer coatings tested in vacuum and air, the AlCrN/TiAlN produced lower COF. The characteristics of the COF produced by AlCrN/TiAlN and AlN/TiN in vacuum and air was similar to those produced by TiAlN and TiN, respectively. This showed that the COF of these nano-multilayer coatings was governed by TiAlN and TiN. AlCrN exhibited the highest wear resistance. TiAlN had the lowest wear resistance. TiN, TiAlN/AlCrN and AlN/TiN which exhibited similar wear resistance, had lower wear resistance than AlCrN but higher wear resistance than TiAlN. In air, increasing the speed from 10 m/min to 100 m/min resulted in a reduction in COF for all coatings, except AlCrN. (C) 2013 The Authors. Published by Elsevier Ltd

Effect of electro-carburisation process on the tribological behavior of mild steel

The effect of carburisation process utilizing Na2e03-NaCI as electrolyte on the microstructure and sliding wear behavior of mild steel had been investigated. The carburisation process was conducted at a constant voltage supply of 4.5 V at 860 ° e for 1 and 3 hours. Sliding tests of the carburised steels were conducted at different loads and speeds under dry, vacuum and oil lubrication conditions. The wear morphology of the sliding tests were analysed. Increasing duration of the carburisation process led to a significant increase in the peak hardness and case depth. The steel specimen carburised for 1 hour had a peak hardness of 910 HV and a case depth of 450 μm. Three hours of carburisation produced higher peak hardness and case depth of 1014 HV and 690 μm, respectively. The hardness were significantly higher than the non-carburised specimen with the hardness of 520 HV. The surface of the carburised specimen was dominated by retained austenite with grain boundaries along with some martensite. Towards the peak hardness, the grain boundaries gradually diminished, and the amount of retained austenite decreased while the amount of martensite increased. In the initial stage of sliding wear test at 10 m/min speed, patches of nascent cavities on the worn surfaces produced by adhesion were formed. These acted as preferential sites for fracture to take place, resulting in a marked increase in the frictional force. Longer carburisation duration also resulted in higher tendency of the carburised layer to form a better anti-wear oxide during sliding. The oxide formed on the worn surface of the specimen carburized for 1 hours was hematite. Both hematite and magnetite known for its better lubricity, were detected on the worn surface of the specimen carburised for 3 hours. The increase in peak hardness and formation of the magnetite enhanced the adhesive wear resistance which in turn reduced the tendency of the specimen to fracture. Longer carburisation duration also resulted in the formation of expanded martensite and shallower grain boundaries with lesser cementite which further enhance the fracture resistance of the carburised specimen. The wear of the counterpart we ball reflected the severity of fractured worn surface on sliding specimen. At 10 m/min speed, severe fracture caused the formation of severe grooving, cavities, undermined and cracked we grains. Whereas, micro-fracture resulted in wear characterised by fine grooves and fewer cavities and undermined we grains. Sliding at 70 m/min speed induced formation of magnetite and hematite on the worn surface of specimen carburised for 1 hour. Surface fracturing was hindered when sliding on carburised specimen. The effect of matrix softening was greatly reduced as compared with non-carburised specimens sliding at the same speed. Protrusion was formed on the we ball sliding on the carburised specimen which replicated from the narrow and deep groove formed on the worn carburised specimen. Under lubricated condition, carburised specimen showed formation of magnetite and hematite on the worn surface at very high load. Cavities was formed owing to the fracture of the oxide on the sliding surface. The oxide debris would either rolled between the gap of the sliding surface, causing reduction in the coefficient of friction or adhered on the mating we ball that induced groove marks on the worn sliding surface. The results obtained, either in dry or lubrication condition, concluded that carburised 3 hours specimen showed better wear and fatigue resistance during sliding

Effect of electro-carburisation process on the tribological behavior of mild steel

The effect of carburisation process utilizing Na2e03-NaCI as electrolyte on the microstructure and sliding wear behavior of mild steel had been investigated. The carburisation process was conducted at a constant voltage supply of 4.5 V at 860 ° e for 1 and 3 hours. Sliding tests of the carburised steels were conducted at different loads and speeds under dry, vacuum and oil lubrication conditions. The wear morphology of the sliding tests were analysed. Increasing duration of the carburisation process led to a significant increase in the peak hardness and case depth. The steel specimen carburised for 1 hour had a peak hardness of 910 HV and a case depth of 450 μm. Three hours of carburisation produced higher peak hardness and case depth of 1014 HV and 690 μm, respectively. The hardness were significantly higher than the non-carburised specimen with the hardness of 520 HV. The surface of the carburised specimen was dominated by retained austenite with grain boundaries along with some martensite. Towards the peak hardness, the grain boundaries gradually diminished, and the amount of retained austenite decreased while the amount of martensite increased. In the initial stage of sliding wear test at 10 m/min speed, patches of nascent cavities on the worn surfaces produced by adhesion were formed. These acted as preferential sites for fracture to take place, resulting in a marked increase in the frictional force. Longer carburisation duration also resulted in higher tendency of the carburised layer to form a better anti-wear oxide during sliding. The oxide formed on the worn surface of the specimen carburized for 1 hours was hematite. Both hematite and magnetite known for its better lubricity, were detected on the worn surface of the specimen carburised for 3 hours. The increase in peak hardness and formation of the magnetite enhanced the adhesive wear resistance which in turn reduced the tendency of the specimen to fracture. Longer carburisation duration also resulted in the formation of expanded martensite and shallower grain boundaries with lesser cementite which further enhance the fracture resistance of the carburised specimen. The wear of the counterpart we ball reflected the severity of fractured worn surface on sliding specimen. At 10 m/min speed, severe fracture caused the formation of severe grooving, cavities, undermined and cracked we grains. Whereas, micro-fracture resulted in wear characterised by fine grooves and fewer cavities and undermined we grains. Sliding at 70 m/min speed induced formation of magnetite and hematite on the worn surface of specimen carburised for 1 hour. Surface fracturing was hindered when sliding on carburised specimen. The effect of matrix softening was greatly reduced as compared with non-carburised specimens sliding at the same speed. Protrusion was formed on the we ball sliding on the carburised specimen which replicated from the narrow and deep groove formed on the worn carburised specimen. Under lubricated condition, carburised specimen showed formation of magnetite and hematite on the worn surface at very high load. Cavities was formed owing to the fracture of the oxide on the sliding surface. The oxide debris would either rolled between the gap of the sliding surface, causing reduction in the coefficient of friction or adhered on the mating we ball that induced groove marks on the worn sliding surface. The results obtained, either in dry or lubrication condition, concluded that carburised 3 hours specimen showed better wear and fatigue resistance during sliding

Technical feasibility of a 1000 MWe pulverized coal power plant under ammonia co-combustion conditions

Ammonia has attracted the attention as a practical way to reach carbon free power generation. Ammonia co-combustion characteristics in 1000MWe pulverized coal power plant was simulated by using Aspen Plus and evaluated under an excess air ratio of 1.0–1.2, air of 2642–3457 ton/hr, coal of 208.2–355.5 ton/hr, ammonia of 0–186.14 ton/hr and various coals. The influence of co-combustion ratios of different coals on emission characteristics and net efficiency was compared. For carbon dioxide emission reduction, the respective CO2 intensity reduction for KPU and BG was 36.44 and 37.76% in calorific value basis, 32.51 and 31.90% in weight basis. The net efficiencies of the power cycle showed a lower decrease as the fuel was supplied on the weight basis compared to the calorific value basis. Based on the obtained results, the KPU on the weight basis showed the lowest net efficiency decrement of 3.1%, but in terms of CO2 intensity reduction, BG on calorific value basis showed most drastic reduction of 37.76%. Consequently, these results showed an effective carbon reduction with ammonia co-combustion and provides a promising solution for the pulverized coal power plants to compass a meaningful reduction of carbon emissions and conservation of combustion efficiency

Recent advances and future prospects of thermochemical biofuel conversion processes with machine learning

Biofuels have been widely recognized as potential solutions to addressing the climate crisis and strengthening energy security and sustainability. However, techno-economic and environmental challenges for the production of biofuels remain and complicated conversion processes and factors, such as materials and process design, need to be taken into consideration for solving the challenges, which is not easy. Machine Learning (ML) has been combined with the theories of thermochemical biofuel conversion processes to achieve accurate and efficient biofuel process modelling. In this review, existing ML applications to predict biofuel yield and composition are critically reviewed. The details of the input and output variables of the developed models for thermochemical biofuel conversion processes were summarized, and their development procedures were compared. Techno-economic analysis results incorporating ML applications in biofuels were also reviewed. Although developed models in literature showed good performance for their targets, respectively, they can hardly be applied to other feedstocks or operating conditions. To overcome the challenge and develop universal model, perspective approaches were suggested in this study. It was suggested that it is essential to develop systematic datasets to support more comprehensive machine learning-based modelling towards practical applications. Potential prospective research and development directions on machine learning-based thermochemical biofuel conversion process modeling were recommended, so that it can assist in the commercialization and optimization of various biofuel conversions leading to a sustainable and circular society

Frictional and wear behaviour of AlCrN, TiN, TiAlN single-layer coatings, and TiAlN/AlCrN, AlN/TiN nano-multilayer coatings in dry sliding

This paper examines the frictional and wear behaviour of AlCrN, TiN, TiAlN single-layer coatings, and TiAlN/AlCrN, AlN/TiN nano-multilayer coatings in dry sliding. Comparative studies on the coatings sliding in air and vacuum environment at different speeds provided important insight on the effect of oxidation and temperature on the frictional and wear behaviour of the coatings. Among all the single-layer coatings tested in vacuum, TiN gave the lowest coefficient of friction (COF), followed by TiAlN and AlCrN. This indicated that TiN was the most lubricous coating. At 10 m/min in ambient air in which oxidation took place, AlCrN gave the lowest COF, followed by TiN and TiAlN. Among the two types of nano-multilayer coatings tested in vacuum and air, the AlCrN/TiAlN produced lower COF. The characteristics of the COF produced by AlCrN/TiAlN and AlN/TiN in vacuum and air was similar to those produced by TiAlN and TiN, respectively. This showed that the COF of these nano-multilayer coatings was governed by TiAlN and TiN. AlCrN exhibited the highest wear resistance. TiAlN had the lowest wear resistance. TiN, TiAlN/AlCrN and AlN/TiN which exhibited similar wear resistance, had lower wear resistance than AlCrN but higher wear resistance than TiAlN. In air, increasing the speed from 10 m/min to 100 m/min resulted in a reduction in COF for all coatings, except AlCrN