Investigation on the Microstructure Hardness for the Hot Compressed Duplex Steel

Effect of microstructure size and type on the hardness for the duplex steel were disclosed by using of optical microscope (OM), scanning electron microscope (SEM) and nanoindenter for the samples hot compressed under different temperature with reduction of 10%, 30%, 50% and 70%. OM and SEM were used to measure the average martensite lamellar width, space and indenter morphology. nanoindenter test characterized the microstructure hardness for the samples under different process. Experiment results show that martensite hardness for the sample hot compressed at 950°C has larger diversity than that of sample hot compressed at 1200°C. The martensite hardness fluctuation range for the sample compressed at 950°C is almost from about 7GPa to 12GPa, while, for the sample compressed at 1200°C, the fluctuation range is basically from about 9GPa to 12GPa. However, the average hardness for the samples hot compressed at 950°C is comparably smaller, which is related with lower quench temperature. The larger martensite hardness fluctuation is mainly related with induced ferrite formation and finer martensite lamellar width. For the ferrite phase, the hardness fluctuation range is lower.

Effect of Alloying Composition on Microstructure and Mechanical Properties of Ultranarrow Gap Welded Joints of U71Mn Rail Steel

A new welding method, ultranarrow gap welding with constrained arc by flux band, is proposed to compensate for the low quality of rail thermite welded joints. This article presents the results of research on the microstructure and mechanical properties of ultranarrow gap welded joints of U71Mn rail steel made using three types of alloying composition content flux bands. Results indicated that the base metal metallographic microstructure consisted mainly of pearlitic, the HAZ was mainly composed of fine pearlite, and the microstructure of the welded bead was composed of acicular ferrite, while the weld grain size decreased as the alloy composition increased. The average hardness noticeably changed in weld metal as the alloy composition increased, and when the alloy composition reached 19%, the hardness was equivalent to the base material. The average hardness value of the HAZ (35.8 HRC) was higher than that of the base metal (24.8 HRC). The tensile strength increased, and the percentage elongation after fracture decreased with increasing alloying composition from 9% to 19%. The impact absorbing energies were decreased as the alloying composition increased. Consequently, all the mechanical properties of rail ultranarrow gap welding were higher than those of the standard requirements of the rail flash welding. And the optimal alloying composition of flux band was 19%.

Effects of Heat Treatment on the Microstructure and Hardness of A356 (AlSi7Mg0.3) Manufactured by Vertical Centrifugal Casting

The A356 alloy has been widely used in automotive components, such as wheels and brake disks, because it is an excellent lightweight material with high corrosion resistance and good mechanical properties. Recently, to reduce the weight of brake disks, the Fe-A356 hybrid brake disk has been suggested. Because brake disk quality is directly related to driving safety, the T4/T6 heat treatment of centrifugally cast A356 alloys were performed to enhance the mechanical properties and reduce micro-segregation. The solid-solution heat treatment followed by annealing caused the formation of Mg-rich intermetallic compounds on the grain boundaries of the Al matrix, decreasing the average hardness of the alloys by 13 HV. In contrast, the solid solution followed by water quenching (T4) reduced the area fractions of the intermetallic compounds and increased the average hardness by 11 HV. The T6 heat-treated A356 alloys, which were influenced by the formation of the Guinier–Preston zone exhibited a relatively higher average hardness, by 18 HV, compared to T4 heat-treated A356 alloys.

The Potential of Al2O3–ZrO2-Based Composites, Formed via CSC Method, in Linear Infrastructure Applications Based on Their Mechanical, Thermal and Environmental performance

Ceramic-ceramic composites have been prepared using the centrifugal slip casting method (CSC). The method has so far been mainly utilized in making ceramic-metal composites. Al2O3–ZrO2 composites have been obtained with different shares of ZrO2, i.e., 15, 50 and 75 vol pct, respectively. Prior to sintering the composite samples, the rheological properties of the casting slips were investigated and thermogravimetric tests were performed. Upon sintering, all three series of the ceramic composites showed a density close to 100 pct and no microcracks or delamination. Phase, microstructural and mechanical investigations were carried out to determine what effect the share of ceramics has on the composites produced. An increase in the share of ZrO2 in the Al2O3–ZrO2 composite leads to a reduction in the growth of Al2O3 grains and a decrease in the average hardness. Cross-sectional hardness testing of the composites showed no evident gradient in any of the samples. Life cycle analysis (LCA) results indicate that the further optimization of the composite formation process, including up-scaling, allows to obtain Al2O3–ZrO2-based pipes possessing more favorable environmental characteristics compared with materials conventionally used for linear infrastructure, which is important in light of the global transformation toward sustainable construction and the circular economy. Graphical abstract

Research on Laser Cladding Co-Based Alloy on the Surface of Vermicular Graphite Cast Iron

To further improve the hardness of the laser cladding layer on the surface of the vermicular graphite cast iron, the structural parameters of the laser cladding Co-base were designed and optimized, and the properties of the clad layer were evaluated using optical microscopy (OM), scanning electron microscopy (SEM), energy spectroscopy (EDS), X-ray diffractometer (XRD), electrochemical workstation, and friction wear equipment. The results show that the average hardness of the molten layer of Ni and Co-based composite cladding layer is 504 HV0.5, which is 0.64 times that of the Co-based cladding layer due to the combined factors of Ni-Cr-Fe equivalent to the dilution of the Ni-based cladding layer to the Co-based cladding layer. Due to the potential difference of the Ni, Cr, and Co elements on the surface of the cladding layer, the self-corrosion potential of the Ni and Co-based composite cladding layer is 1.08 times that of the Co-based cladding layer, and the self-corrosion current density is 0.51 times. Laser cladding Co-based cladding layer has high corrosion resistance. Under the influence of plastic deformation and oxidative wear of the cladding layer of the Ni and Co-based composite cladding layer, the wear amount of the cladding layer of the Ni and Co-based composite cladding layer is less.

Influence of High-Pressure Torsion on the Microstructure and Microhardness of Additively Manufactured 316L Stainless Steel

High-pressure torsion (HPT) is known as an effective severe plastic deformation (SPD) technique to produce bulk ultrafine-grained (UFG) metals and alloys by the application of combined compressive force and torsional shear strains on thin disk samples. In this study, the microstructures and microhardness evolution of an additively manufactured (AM) 316L stainless steel (316L SS) processed through 5 HPT revolutions are evaluated at the central disk area, where the effective shear strains are relatively low compared to the peripheral regions. Scanning electron microscopy (SEM) analysis showed that the cellular network sub-structures in AM 316L SS were destroyed after 5 HPT revolutions. Transmission electron microscopy (TEM) observations revealed non-equilibrium ultrafine grained (UFG) microstructures (average grain size: ~115 nm) after 5 revolutions. Furthermore, energy dispersive x-ray spectroscopy (EDX) analysis suggested that spherical Cr-based nano-silicates are also found in the as-received condition, which are retained even after HPT processing. Vickers microhardness (HV) measurements indicated significant increase in average hardness values from ~220 HV before HPT processing to ~560 HV after 5 revolutions. Quantitative X-ray diffraction (XRD) patterns exhibit a considerable increase in dislocation density from ~0.7 × 1013 m−2 to ~1.04 × 1015 m−2. The super-high average hardness increment after 5 HPT revolutions is predicted to be attributed to the UFG grain refinement, significant increase in dislocation densities and the presence of the Cr-based nano-silicates, according to the model established based on the linear additive theory.

On the Structure and Properties of AlMgB14-TiB2 Composites Obtained from SHS Powders by Spark Plasma Sintering

AlMgB14-TiB2 composite materials were fabricated by self-propagating high-temperature synthesis (SHS) followed by spark plasma sintering of the obtained SHS products. It was found that, during the SHS, the AlMgB14 phase is formed at a donor (Ti + 2B) to acceptor (Al12Mg17-B) mass ratio of 3:7 and 4:6, respectively. The specimen sintered from the SHS powder with the donor:acceptor mass ratio of 5:5 at a temperature of 1470 °C has a uniform skeletal structure. The average hardness of the obtained specimen is 30.1 GPa.

Effect of Artificial Aging on Mechanical and Tribological Properties of CAD/CAM Composite Materials Used in Dentistry

With easy-to-process 3D printing materials and fast production, the quality of dental services can be improved. In the conventional procedure, the dentist makes temporary crowns directly in the patient’s mouth, e.g., from the most commonly used bis-acrylic composites. Temporary crowns made directly in the office without the use of CAD/CAM are often of inferior quality, which directly results in impaired hygiene, poorer masticatory mechanics, greater deposition of plaque, calculus and sediment, and may adversely affect periodontal and gum health. The mechanical strength, resistance to aging and abrasion of 3D printing materials are higher than those of the soft materials used in conventional methods. This translates into durability. The patient leaves the surgery with a restoration of higher utility quality compared to the conventional method. The objective of the paper was to determine the influence of aging in artificial saliva of AM (additive manufacturing) orthodontic composites on their functional properties. For the purpose of the study, fillings well-known worldwide were selected. These were traditional UV-curable resins (M I, M II, M III, M V) and a hybrid material based on a UV-curable resin (M VI). Samples were stored in artificial saliva at 37 ± 1 °C in a thermal chamber for 6 months. Indentation hardness, frictional tests and sliding wear measurements were conducted. A comparison between various materials was made. Descriptive statistics, degradation coefficients, H2E, Archard wear and specific wear rate were calculated. The Weibull statistical test for indentation hardness was performed and Hertzian contact stresses for the frictional association were calculated for unaged (M I, M II, M III, M V, M VI) and aged (M I AS, M II AS, M III AS, M V AS, M VI AS) samples. M I exhibited the lowest average hardness among the unaged materials, while M III AS had the lowest average hardness among the aged materials. Comparably low hardness was demonstrated by the M I AS material. The coefficient of friction values for the aged samples were found to be higher. The lowest wear value was demonstrated by the M I material. The wear resistance of most of the tested materials deteriorated after aging. The M VI AS material had the highest increase in wear. According to the results provided, not only the chemical composition and structure, but also aging have a great impact on the indentation hardness and wear resistance of the tested orthodontic materials.

Influence of Welding Speed on Hard-facing Deposited by MIG Welding

Hard-facing is one of processes for repairing metallic surface of equipment or parts of machinery that are lost due to outworn mechanism. Therefore, hard-facing requires suitable variables to obtain the hardest hard-faced metals. This research aimed to study influence of welding speed on hard-facing affecting microstructure and hardness of the hard-faced metals on JIS-S45C carbon steel with MIG welding. According to the experiment, hard-facing with welding speed at 250 mm/min contained dilution of elements lower than welding speed at 200 and 300 mm/min. Therefore, the hard-faced metals contained elements the most including Silicon 2.25 %, Chromium 6.12 % and Manganese 0.51 %, which affected the enhancement of mechanical properties of welded metals. The hard-faced metal had highest average hardness at 705.9 HV0.1.

Microstructure and Properties of ER50-6 Steel Fabricated by Wire Arc Additive Manufacturing

In this paper, ER50-6 steel was fabricated by wire arc additive manufacturing (WAAM) with an A-W GTAW system. The microstructure, mechanical properties, and corrosion behaviors of ER50-6 steel by WAAM were studied. The results showed that, with the GMAW current increased, from the bottom to the top of the sample, the microstructure was fine ferrite and granular pearlite, ferrite equiaxed grains with fine grains at grain boundaries, and columnar ferrite, respectively. The average hardness in the vertical direction of samples 1# and 2# was 146 and 153 HV, respectively. The hardness of sample 2# increased because of the refinement of grain. The pores in the sample increased as the bypass current increased. The higher bypass current also has a deterioration effect on the corrosion behavior of ER50-6 steel.