The effect of the beam scanning speed on part microstructures in the powder-bed electron beam additive manufacturing (EBAM) process was investigated in this research. Four levels of the beam speed were tested in building EBAM Ti–6Al–4V samples. The samples were subsequently used to prepare metallographic specimens for observations by optical microscopy and scanning electron microscopy. During the experiment, a near-infrared thermal imager was also used to acquire build surface temperatures for melt tool size estimates. It was found that the X-plane (side surface) shows columnar prior β grains, with the width in the range of about 40–110 µm, and martensitic structures. The width of columnar grains decreases with the increase of the scanning speed. In addition, the Z-plane (scanning surface) shows equiaxed grains, in the range of 50–85 µm. The grain size from the lowest beam speed (214 mm/s) is much larger compared to other samples of higher beam speeds (e.g., 376–689 mm/s). In addition, increasing the beam scanning speed will also result in finer α-lath. However, the porosity defect on the build surface also becomes severe at the highest scanning speed (689 mm/s).

Selective laser melting (SLM) process was used to prepare the nanocrystalline titanium carbide (TiC)-reinforced Inconel 718 matrix bulk-form nanocomposites in the present study. An in-depth relationship between SLM process, microstructures, properties, and metallurgical mechanisms was established. The insufficient laser energy density (η) input limited the densification response of shaped parts due to the formation of either larger-sized pore chains or interlayer micropores. The densification of SLM-processed part increased to a near-full level as the applied η was properly settled. The TiC reinforcements generally experienced successive changes from severely agglomerated in a polygon shape to the uniformly distributed with smoothened and refined structures on increasing the applied η, while the columnar dendrite matrix exhibited strong epitaxial growth characteristic concurrently. The optimally prepared fully dense part achieved a high microhardness with a mean value of 419 HV0.2, a considerably low friction coefficient of 0.29, and attendant reduced wear rate of 2.69 × 10−4 mm3/N m in dry sliding wear tests. The improved densification response, SLM-inherent nonequilibrium metallurgical mechanisms with resultant uniformly dispersed reinforcement microstructures, and elevated microhardness were believed to be responsible for the enhancement of wear performance.

Nanoporous tungsten oxide films were synthesized by an anodic oxidation process in aqueous NaF/HF electrolytes. The tungsten films were deposited by the radio frequency magnetron sputtering method on sapphire substrates, and the anodic oxidation process was conducted in a dual-electrode reaction chamber with graphite electrode. The effects of processing parameters (anodic voltage, time, temperature, and the operation distance) on the morphology and porosity of the synthesized films were investigated experimentally. The samples were characterized by x-ray diffraction and scanning electron microscopy. The results showed that the pore diameter and porosity increased gradually with increasing anodic voltage, whereas the “wall” of the pore was subjected to electric breakdown at 60 V, and the pore diameter and porosity decreased. The pore diameter and porosity showed an early increased and later decreased state as the operation time and distance are increased. The sensitive response in the resistive method is reaction-dominated type and is exhibited as a linear relationship as a function of hydrogen gas concentration. The response toward 500 ppm hydrogen in air is up to 15.1 with a response time of 10 min at 200 °C.

Ultrasonic consolidation is a rapid manufacturing process for metal matrix composite (MMC) preimpregnated composite (prepreg) tapes or foils. One of the main advantages of this manufacturing technique over traditional MMC methods is the ability to produce multimaterial structures through the layer-by-layer build-up procedure. The interface of an ultrasonically consolidated bimaterial interface has not been studied on the nanometer scale through transmission electron microscopy (TEM), which can help better understand the bonding mechanisms. An ultrasonically consolidated copper–aluminum (Cu–Al) interface was explored through TEM, through which a 1-µm recrystallized subgrain region was observed on the aluminum side and dislocation pile-up was viewed between the subgrain and bulk aluminum interface. Phase changes were suspected due to varying contrast bands parallel to the Cu–Al interface and were confirmed through an x-ray energy dispersive spectroscopy (XEDS) linescan. An apparent diffusion coefficient was calculated, which supported bulk diffusion at the measured welding temperature of 493 °C and subgrain size of 20–50 nm.

H13 tool steel was deposited using the additive manufacturing technique Direct Metal Deposition to produce a part having a wedge geometry. The wedge was characterized both in terms of microstructure and residual stress. It was found that phase transformations were significantly influencing the microstructure, which was then linked to the residual stress distribution as seen in Fig. 8. The residual stress distribution was found to be opposite to that reported in the literature. This was attributed to the low temperature martensitic phase transformation of the H13 tool steel and the subsequent tempering of the microstructure with an increasing number of layers of deposited material. The high hardness and compressive residual stress of the top 4 mm of the wedge are ideal in die casting and forging dies, as it will resist thermal fatigue. It also has a hardness higher than that produced by typical heat treatment processes.

Cube-shaped IN718 samples were produced by selective electron beam melting (SEBM) with varying beam power, deflection speed, and beam spot size. Process parameter windows were identified where fully dense samples are obtained with no surface unevenness. High deflection speeds were demonstrated to result in smaller demand of area energy. This result is explained by the reduced time for heat dissipation into the substrate during hatching. The grain structure was strongly affected by SEBM process parameters. Under certain conditions, epitaxial growth over many layers and well-developed columnar grain structures were obtained with a polycrystalline substrate plate. A more defocused beam led to a lower melt pool temperature and shallower melt pool geometry where maximum temperature gradients and solidification rates were more or less in parallel with the building direction and primary dendrite arm orientation. These conditions help to suppress grain nucleation ahead of the nucleation front as vigorous melt movement, fragmentation of dendrites, and tertiary arm growth are suppressed.

Selective laser sintering (SLS) is a rapidly developing additive manufacturing technique, with advantages in flexibility and low material waste. Many parameters used in a SLS process are determined by powder type: blended powders have limitations due to wetting and diffusion, while prealloyed powders require processing in a small temperature range dictated by the alloy composition. As an alternative to these, a coated powder was fabricated by electrochemical means. This tin–copper composite powder was compared with a blend of tin and copper powders, using metallographic, crystallographic, and thermal analysis techniques as well as SLS. It was found that, because of the uniform distribution of liquid and increased contact between phases in the composite powder, sintering took place in the composite powder but not in the blend. After a homogenization treatment, mechanical testing of the sintered samples showed that the strength and ductility were comparable to high-porosity materials produced using other techniques.

A 5 kW continuous wave fiber laser welding system was used to deposit INCONEL® alloy 718 (IN718) on service-exposed IN718 parent metal (PM) substrates using filler wire addition. The microstructure of the deposits was characterized in the fully heat treated condition. The service-exposed IN718 PM and the direct laser deposited (DLD) specimens were then evaluated through room temperature tensile testing. The yield and tensile strengths were well above the minimum values, as defined in the aerospace specifications AMS 5596K and 5663M. However, the ductility at room temperature of the DLD and DLD-PM samples was slightly lower than that specified in AMS 5596K and 5663M. The tensile fracture surfaces of the service-exposed IN718 PM, DLD, and DLD-PM specimens were analyzed using scanning electron microscopy (SEM), and the tensile failure mechanisms are discussed in detail, particularly for the important roles of the secondary particles (MC carbides) and intermetallics (platelet Ni3Nb-δ and Laves phases).

CoCrMo alloy was deposited on a metallic substrate using laser engineered net shaping (LENS™) – a laser-based additive manufacturing technique. Several samples with five layers of deposit were fabricated at different combinations of laser power, powder feed rate, and scan velocity to study their influence using L4 Orthogonal array. The deposits were evaluated for their microstructure, hardness, wear resistance, and electrochemical performance. Grey relational grade analysis and analysis of variance were applied to identify optimum process parameters. The x-ray diffraction and microstructural analysis of the deposits showed uniform and fine microstructural features. Our experimental results revealed that the coatings fabricated using high laser power (350 W), low powder feed rate (5 g/min), and high scan velocity (20 mm/s) provide the highest hardness (446 ± 2.87 Hv) and wear resistance (1.80 ± 0.0007 mm3/Nm). However, the corrosion resistance was observed to be high for the deposits fabricated using low laser power (200 W), low powder feed rate (5 g/min), and low scan velocity (10 mm/s).

Ti–6Al–4V parts made by the additive manufacturing (AM) technique selective laser melting (SLM) generally show poor ductility due to their fine martensitic microstructure. This study was designed to assess whether a more suitable microstructure can be obtained when long laser/material interaction times are used. As-fabricated components with an α + β microstructure were produced and characterized with various microscopy techniques. The microstructural evolution was discussed in relation to the build platform temperature, the cyclic reheating, and the thermal stresses that developed during the process. The hardness of the samples was also evaluated and discussed. The hardness varied in relation to the different microstructure morphologies observed in the samples and different partitioning of the alloying elements. This study indicates a methodology through SLM to obtain Ti–6Al–4V with an as-deposited α + β microstructure which is more desirable than that the typical fully martensitic microstructure typically obtained after SLM.

The iron aluminide Fe3Al has been successfully processed by selective laser melting (SLM) and laser metal deposition (LMD). Process parameters have been determined by which defect free and dense (>99.5%) samples were produced. However, due to the low thermal conductivity of Fe3Al, preheating the substrate to 200 °C was necessary to prevent cracking during cooling. Microstructural characterization by electron backscatter diffraction (EBSD) showed that in spite of the high cooling rates large elongated grains grew in the building direction, more distinctive for SLM than for LMD. These grains show a continuous change in the crystallographic orientation. Evaluation of the compressive flow stress showed that the anisotropic microstructure results in anisotropic mechanical properties, depending whether the samples are loaded in building direction or perpendicular to it. The alloy shows a very high strength up to 600 °C and – concerning the coarse microstructure – becomes ductile already at low temperatures.

The effect of annealing on the tribological and corrosion properties of Al–12Si samples produced by selective laser melting (SLM) is evaluated via sliding and fretting wear tests and weight loss experiments and compared to the corresponding material processed by conventional casting. Sliding wear shows that the as-prepared SLM material has the least wear rate compared to the cast and heat-treated SLM samples with abrasive wear as the major wear mechanism along with oxidation. Similar trend has also been observed for the fretting wear experiments, where the as-prepared SLM sample displays the minimum wear loss. On the other hand, the acidic corrosion behavior of the as-prepared SLM material as well as of the cast samples is similar and the corrosion rate is accelerated by increasing the heat treatment temperature. This behavior is due to the microstructural changes induced by the heat treatment, where the continuous network of Si characterizing the as-prepared SLM sample transforms to isolated Si particles in the heat-treated SLM specimens. This shows that both the wear and corrosion behaviors are strongly associated with the change in microstructure of the SLM samples due to the heat-treatment process, where the size of the hard Si particles increases, and their density decreases with increasing annealing temperature.