In this paper, we study the energy absorption of metamaterials composed of unit cells whose special geometry makes the cross-sectional area and the volume of the bodies generated from them constant (for the same enclosing box dimensions). After a parametric description of such special geometries, we analyzed by finite element analysis the deformation of the metamaterials we have designed during compression. We 3D printed the designed metamaterials from plastic to subject them to real compression. The results of the finite element analysis were compared with the real compaction results. Then, for each test specimen, we plotted its compaction curve. By fitting a polynomial to the compaction curves and integrating it (area under the curve), the energy absorption of the samples can be obtained. As a result of these investigations, we drew a conclusion about the relationship between energy absorption and cell number.

This study demonstrates the use of simulation in the design of induction hardening coils. It compares three coil geometries, two of which leverage the flexibility of 3D printing. The paper explains how to set up and run the simulations in order to predict temperature fields, hardness profiles, and microstructure distributions in the workpiece. Based on the simulations, the conventionally manufactured coil and one of the two 3D-printed coils do not achieve the desired martensitic microstructure everywhere along the surface of the workpiece. In the case of the 3D-printed coil, the simulations show that the workpiece overheats in an area where its diameter abruptly changes. To fix the problem, the coil was adapted with an additional winding that carries current in the opposite direction. Simulations show that the redesign reduces hot spot temperature by more than 200 °C, producing the desired microstructure in that area of the workpiece and a more uniform hardness profile.

Usually bainitic microstructures exhibit good toughness and austempering is typically the preferred heat treatment when toughness is the primary requirement of the component. Several reports have shown such characteristics when compared to tempered martensite. High carbon steel may exhibit brittle characteristics but it is a good steel with respect to mechanical properties and wear resistance. The objective of this study was to compare the impact properties of AISI O1, a high carbon tool steel as VND in Brazil. This was done by comparing Charpy impact strength under different heat treatment cycles. Tempered martensite and bainite was obtained at 350°C after holding at temperature for 20, 40, and 60 minutes. Since hardness influences impact behavior, comparative studies were performed at the same surface hardness level. Results show a low absorbed energy for the austempered samples which for this temperature is independent of the holding time.

The paper considers a process of induction heating of metallic billets prior to hot forming and heat treatment. The main goal of the presented research is a development of novel subject-oriented computer modeling strategy to optimize various induction heating operations using real-life quality criteria. Intricacies of interrelated nature of electromagnetic, temperature and thermal stresses fields during induction heating of metallic billets will be discussed. The model has an interface adapted to optimization procedures. Optimization of temperature patterns is solved using unique alternative optimization method. Computational results for optimal heating of steel cylindrical billets are shown as examples of practical applications of this modeling technology.

The 2524 aluminum alloy was cold rolled to 70% reduction and then annealed at 500? for 0.5h in an air furnace with a heating rate of 5?/min and in a salt bath with a heating rate of 75?/s, respectively. The effect of heating rate on the microstructure, tensile properties and fatigue crack growth (FCG) rate of the alloy was investigated. The microstructure and mechanical properties of the alloy were studied by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical microscopy (OM), tensile and FCG rate tests. In the case of slow heating the alloy exhibited a coarse elongated grain structure (~75μm), while a fine equiaxed grain structure (~13μm) was obtained in the case of rapid heating. The sheet annealed with rapid heating has slightly higher tensile strength and yield strength, but a slightly lower elongation than the sheet annealed with slow heating. The FCG rate of the sheet annealed with slow heating is 20% lower than the sheet annealed with rapid heating.

The powder injection molding process is used to manufacture parts with complex shapes and high production demand. In orthodontic and medical applications, in which high hardness and corrosion resistance are required, 17-4 PH stainless steel is used mainly by this forming technique. The sintering atmosphere is responsible for controlling the chemical reactions that occur during material densification and is critical to the ultimate product quality. This research evaluated the influence of the sintering atmosphere on the hardness and corrosion resistance of this type of steel. The removal of the primary binder was conducted by chemical extraction by using a solvent with less environmental impact which has proved to be suitable for this purpose. The subsequent binder thermal extraction was performed by heating at temperatures of 250 and 450 °C and afterwards to 900 °C to initiate sintering. Nitrogen, vacuum and hydrogen atmospheres were used with sintering temperatures at 1250 and 1330 °C with 30 and 60 minute time step. It was shown that the densities achieved in hydrogen and vacuum atmospheres are similar and suitable by the regulations, whereas the nitrogen atmosphere resulted in lower performance. The hardness and corrosion resistance obtained with the use of hydrogen and vacuum atmospheres were also higher than those obtained for samples sintered in the nitrogen atmosphere.

Ductile cast iron can be heat-treated to obtain a significant property improvement austempering, resulting in Austempered Ductile Iron (ADI). Performance can be further improved by using boronized surface layers which are capable of reaching high hardnesses (2100 HV). In this work, samples of nodular cast iron alloyed with copper, copper-nickel and copper-nickel molybdenum were borided in a salt bath (borax + aluminum) at temperatures 850, 900 and 950 °C for 2 and 4 hours. After these treatments, the samples were directly austempered from the boriding temperature in salt baths at temperatures of 240, 300 and 360°C (boroaustempering) which avoided the need for a subsequent reheating for such processing. The boriding treatment produced uniform layers with thicknesses in the range 35-130 micrometers and hardness in the range from 1300 to 1700 HV.

Gray cast iron is primarily used for its low cost, high damping capacity, and excellent machinability. These properties are attributed to the presence of free graphite and the high fluidity of the molten metal, which allows for the easy casting of complex parts with thin walls. Applying suitable coatings can enhance wear resistance and broaden the material's range of applications. Niobium carbide, known for its high hardness, is a promising candidate for this purpose. In this study, samples of gray cast iron with the composition 3.47% C, 2.39% Si, 0.55% Mn, 0.15% Ni, 0.65% Cu, and the balance Fe were subjected to a niobizing powder thermo-reactive diffusion treatment. The coating mixture consisted of ferro-niobium, NH 4 Cl, and Al 2 O 3 , and the treatment was conducted at 900 °C for 2 hours. The resulting layers exhibited hardness values of 2000 HV, characteristic of niobium carbides. Micro-adhesive and micro-abrasive wear tests showed a significant increase in wear resistance due to this treatment.

Boriding thermochemical treatment produces layers with high hardness which improves the tribological performance of ductile cast iron while the austempering treatment improves the mechanical performance of the substrate. In this work, samples of the ductile cast iron alloyed with copper, copper-nickel and copper-nickel-molybdenum were borided in a salt bath (borax + aluminum) at temperatures of 850, 900 and 950°C during 2 and 4 hours. The data for the layers obtained were used to determine the diffusion coefficients and activation energies of this process. The results of the calculated diffusion coefficients were similar to those obtained by the direct measurements of the layer thicknesses. For the sample alloyed with Cu or Cu-Ni the activation energy obtained was 141.27 kJ/mol, and for the sample alloyed with Cu-Ni-Mo the value was 212.98 kJ/mol. The statistical parameters and the correlation coefficients (R) showed satisfactory agreement.

The use of high hardness surface layers can extend the life of components such as molds and dies by increasing their wear resistance. However, corrosion and oxidation resistance are also important to improve the durability of the components, especially for those that work under more demanding environments. In this work, samples of AISI H13 tool steel for hot work were borided by the pack cementation process, producing uniform and high hardness layers (1400-1800 HV). Afterwards the samples were subjected to a quasi-isothermal oxidation testing at 550 °C, the same working temperature of H13 steel in aluminum extrusion dies. Throughout the test, the mass gain of the untreated substrate, used for comparison, was 100%, while the borided sample treated at 900 °C for 2 hours had mass gain of 83% and the sample treated at 1000 °C for 4 hours presented a mass gain of 43%. The oxidation coefficients of the borided samples were similar, indicating similar oxidation kinetics but different from the untreated substrate.

Precipitation-hardening stainless steels are iron-nickel chromium alloys containing precipitation hardening elements such as aluminum, titanium, niobium and copper. In this work, heat treatment of a novel precipitation hardening stainless steel using niobium as a forming element for the hardening precipitates in order to increase its surface hardness and wear resistance was performed. The steel composition was 0.03C - 0.22Si - 17.86Cr - 3.91Ni - 2.19Mo - 1.96Nb (in wt%). The samples were solubilized at 1100 °C for 2 hours. Cooling was done in oil and the samples were subsequently aged at 500, 550 and 600 °C. The solubilized samples exhibited an average hardness of 30 HRc and after the aging treatments, the hardness increased to 46 HRc. The hardness increases during the aging treatments were very fast. A 5 minute treatment achieved hardness levels that were close to the maximum obtained for this alloy. Niobium was an efficient precipitation hardeners forming a Laves phase of the type Fe 2 Nb.