Ductility dip cracking (DDC) is a detrimental solid-state cracking phenomenon that can occur during welding of copper-nickel (Cu-Ni) alloys used in naval vessels. The presence of these cracks has several deleterious effects, including reduced fatigue life and increased susceptibility to corrosion. The mechanism of DDC remains highly debated and understudied, especially in material systems outside of Ni-Cr-Fe alloys. The predominant mechanisms that have been proposed include: 1. Grain boundary sliding, 2. Precipitate-induced strain, and 3. Impurity element segregation. In the present body of research, thermal-mechanical testing over a wide range of strain rates and temperatures was performed using a Gleeble 3500. Both flow-stress and fracture morphology of wrought 70/30 Cu- Ni are considered. Following fracture, microstructural analyses using both scanning electron microscopy and optical microscopy were conducted to observe and quantify intergranular cracking and fracture surface features. Results show a strong correlation among fracture morphology, ductility, and temperature.

Decarburization of steel parts during heat treating results in a lower surface hardness, undesirable residual stress profiles, and poor part performance. Significant effort has been made towards preventing decarburization and determining the impact of annealing time and temperature on decarburization rate. Much of the published research has focused on medium carbon steels, ranging from 0.3wt% C to the eutectoid composition. The goal of the current research is to determine decarburization rates for steels with carbon concentrations above the eutectoid concentration. AISI 52100 steel was heated in air for 12, 24, and 36 hours at three temperature ranges (below A 1 , above A cm , and between A 1 and A cm ). Optical microscopy was used to determine the carbon concentration as a function of depth from the surface. The diffusion coefficients of carbon in austenite and ferrite plus cementite phase assemblages were calculated. These diffusion coefficients can be used in a finite difference simulation to predict decarburization at different temperatures and times.

Carburization is a common method of hardening steel surfaces to be wear-resistant for a wide range of mechanical processes. One critical characteristic of the carburization process is the increase in carbon content that leads to the formation of martensite in the surface layer. Combustion and spark-OES are two common methods for determination of carbon in steels. However, these techniques do not effectively separate carbon from near surface contaminants, carburized layers, and base material composition. Careful consideration of glow discharge spectroscopy as a method of precisely characterizing carbon concentration in surface layers as part of a production process should be evaluated in terms of how the resulting data align with other common analytical and metallurgical measurements. When used together, glow discharge spectroscopy, optical microscopy, and microhardness testing are all useful, complementary techniques for characterizing the elemental composition, visually observable changes in material composition, and changes in surface hardness throughout the hardened case, respectively. Close agreement between related measurements can be used to support the use of each of these techniques as part of a strong quality program for heat treatment facilities.

The AISI 440B (DIN 1.2210, X90CrMoV18) steel is one of the hardest among martensitic stainless steels. This type of steel is used in a variety of industrial applications where wear and corrosion are determinant, such as molds, parts and tools for the automotive and biomedical industries. Their superior mechanical properties are due to its high carbon (0.75-0.95 % C) and chromium (16-18% Cr) contents. Suitable coatings can increase wear resistance and expand these materials usability range. Boride coatings, with their high hardness and wear resistance are good candidates for this purpose. Boride layers were obtained by boriding treatment in a salt bath (a mixture of sodium borate and aluminum). The layer properties, such as hardness, thickness, layer/substrate interface morphology and phases formed are influenced by steel composition. In this work, the layers produced on AISI 440B steel were harder, thinner, with a smoother interface when compared to plain carbon steels due the larger amount of alloying elements. In order to evaluate mechanical properties of borided layers in samples of stainless steel AISI 440B, Optical Microscopy (OM) microstructural analysis, Vickers microhardness tests and micro-adhesive and micro-abrasive wear resistance tests were performed. The layers produced exhibited a hardness close to 2250 HV and excellent wear resistance far superior to that of substrate.

In the present study unalloyed spheroidal graphite iron was compared with a sample alloyed with copper and nickel (Cu- Ni). Samples of those materials were treated in salt bath (a composite of sodium borate, aluminum, iron-niobium and/or iron-vanadium) at 1000 °C for 2 hours. This resulted in layers of niobium carbide (NbC), vanadium carbide (VC) and ternary carbide of niobium and vanadium (NbVC2). Characterization of these layers was obtained by optical microscopy, X-ray diffraction and microhardness Vickers. The microhardness and the thickness results were statistically analyzed by the two factors variance analysis method. The efficiency of the layered surface in increasing corrosion resistance was demonstrated by submitting it to potentiodynamic polarization corrosion tests.

Ti-6Al-4V alloy is characterized to be sensitive to heat treatment and deformation. This paper focuses on microstructural evolution and variation in mechanical properties with respect to the deformation and change in the heat treatment cycle. Different heat treatment cycles such as mill annealing, solution treatment and beta solution treatment followed by annealing were carried out on deformed and undeformed Ti-6Al-4V samples. Heat treated samples were studied using optical and scanning electron microscopy. Also different mechanical tests (i.e. tensile test, fracture toughness test) were conducted and results were analyzed. Large variation in mechanical properties and microstructures were found out with different heat treatment cycles. Fracture toughness was found to be high for beta solution treatment samples than the mill annealed and solution treated samples and the reason for the same has been analyzed.

Discovering microstructural features of white layer in a nitrided part has appealed to many scientists and researchers. A slight change in microscopic properties can bring a huge difference in their macro-scale behavior. A thorough knowledge of the compound (the white layer) and of the diffusion zone will enable materials scientists to monitor the grain size (the phases within the material), which alter the macro-scale toughness and strength and finally the amount of porosity. Unlike carburizing, which is a more matured technology, nitriding specifications are genetically stated as surface hardness and hardness at depths. No constituents or type and percent of compounds are mentioned. This paper will attempt to address methodologies used to identify different constituents of both the compound and the diffusion layers of a nitrided part. Three different materials have been heat treated for this study. Three different methods of investigation were used: optical microscopy, electron dispersive spectroscopy (EDS) and electron probe microanalysis (EPMA). This is the beginning of a series of investigations which are underway. In this article, information already known will be the starting point. In future articles, more in depth investigation of the white layer and of the diffusion zone will be shown.

This article addresses an investigation of the influence of plastic deformation on low-temperature surface hardening by gaseous nitriding of three commercial austenitic stainless steels: AISI 304, EN 1.4369 and Sandvik Nanoflex with various degrees of austenite stability. The materials were plastically deformed to different equivalent strains by uniaxial tension. Gaseous nitriding of the strained material was performed in ammonia at atmospheric pressure in the temperature range 693-703 K (420-430°C). Microstructural characterization of the as-deformed states and the nitrided case included X-ray diffraction analysis, reflected light microscopy and microhardness indentation. The results demonstrate that a case of expanded austenite develops and that, in particular, the presence of strain-induced martensite in the initial (deformed) microstructure has a large influence on the nitrided zone.

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.