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This study shows that the mechanical strength of the composite of Fe matrix and titanium carbide (TiC) ceramic particles is significantly enhanced with addition of molybdenum (Mo) atoms. TiC reinforced Fe (Fe-0.2C-7Mn) composites with and without Mo were fabricated by a liquid pressing infiltration (LPI) process and the effect of Mo on interfacial properties of TiC–Fe composite was investigated using atomic probe tomography (APT) analysis, molecular dynamics (MD) simulations, first-principle density functional theory (DFT), and thermodynamic calculations. First, DFT calculations showed that total energies of the Mo-doped TiC–Fe superlattices strongly depend on the position of Mo defects, and are minimized when the Mo atom is located at the TiC/Fe interface, supporting the probable formation of MoC-like interphase at the TiC/Fe interface region. Then, APT analysis confirmed the DFT predictions by finding that about 6.5 wt.% Mo is incorporated in the TiC–Fe(Mo) composite and that sub-micrometer thick (Ti,Mo)C interphase is indeed formed near the interface. The MD simulations show that Mo atoms migrate to the Mo-free TiC–Fe interface at elevated temperatures and the mechanical strength of the interface is considerably enhanced, which is in good agreement with experimental observations.

This study investigated the effect of the hydrogen charging time on the hydrogen embrittlement of hot-rolled and accelerated-cooling treated API X70 steel by using the electrochemical hydrogen charging method. Tensile and V-notch Charpy impact test were completed for the specimens of hydrogen charged for 0, 2, 4, and 10 h, and then microstructural observation were performed. The tensile and yield strength tended to decrease slightly and the total elongation started to decrease rapidly up to 2 h charging time and then these gradually decreased with the hydrogen charging time. The post-uniform elongation increased slightly after the holding time of 2 h due to the occurrence of two-step stress reduction phenomenon and its mechanism has suggested. The effect of the hydrogen embrittlement on impact absorption energy according to the hydrogen charging time were also investigated. The fracture surface of the hydrogen charged ones are generally composed of cleavage fracture surfaces. It was demonstrated that the external cracks were formed on the outside of tensile tested specimen and the external shape of the fracture portion was fractured without large elongation at hydrogen charged specimens.

Cement mixture with calcite-ettringite seeds (CE seeds) was investigated in terms of early hydration and mechanical property. The ettringite crystals of ettringite seeds (E seeds) exhibited needle-...

For the development of a lightweight, high-strength, and oxidation-resistant steel matrix composite, titanium carbide (TiC) reinforced SUS431 metal matrix composites (MMCs) were proposed in this study. TiC–SUS431 composite, which is 25.5% lighter than SUS431, was successfully fabricated by a liquid pressing infiltration (LPI) process. The TiC particles are homogenously distributed in the SUS431 matrix without apparent pores or impurities. Effect of TiC particle size on the anti-oxidation properties of the composites was also investigated in the research. The mass gain of the tested TiC(1 μm)–SUS431 composite, held at 700 °C for 50 h in an air environment, decreased by about 90% compared to that of the TiC(3 μm)–SUS431 composite, which indicates improved oxidation resistance originating from the formation of a thermally stable thin Ti oxides on the composite.

The corrosion properties of Fe-Cr-Mn-C-N high interstitial austenitic stainless cast steels were investigated for down-hole application in sour environments. The two cast alloys contained 0.66% and 0.71% of total nitrogen and carbon. The corrosion properties of the alloys that were solution-treated and fast-cooled were directly responsible for high corrosion resistance in NaCl solution, including resistance to pitting corrosion resulting from a better distribution of chromium chemical compound in the high interstitial stainless cast steel. However, the sour corrosion resistance of the alloys decreased with the fast cooling rate, which can be attributed to the increased amount of ferrite containing Fe2+, which causes iron sulfide precipitate formation in H2S.

In order to explore the possibility of using carbon nanotube (CNT) to introduce and control the temperature coefficient of resistance (TCR) of metal matrix composite, relatively thick and short multi-walled CNTs (MWCNTs) were introduced in the metal matrix with in-situ formation of chromium carbide (Cr7C3) at the CNT/copper (Cu) interface. We demonstrate that incompatible properties such as electrical conductivity and TCR can be achieved simultaneously by introducing MWCNTs in the Cu matrix, with control of the interfacial resistivity using the MWCNT/Cr7C3–Cu system. High electrical conductivity of 94.66 IACS and low TCR of 1,451 10–6 °C−1 are achieved in the 5 vol.% MWCNT–CuCr composite. In-situ formation of Cr7C3 nanostructures at the MWCNT/Cu interface by reaction of diffused Cr atoms and amorphous carbon of MWCNTs would assist in improving the electrical properties of the MWCNT–CuCr composites.

Titanium carbide (TiC) reinforced tool steel matrix composites were successfully fabricated by a liquid pressing infiltration process and research was subsequently conducted to investigate the composites’ oxidation resistance. The mass gain of the tested TiC–SKD11 composite held at 700 °C for 50 h in an air environment decreased by about 60%, versus that of the SKD11, which indicates improved oxidation resistance. Improved oxidation resistance of the TiC–SKD11 composite originates from uniformly reinforced TiC, with a phase transition to thermodynamically stable, volume-expanded TiO 2 .

The anisotropy of the Nd2Fe14B powder is originated during the creation of a fine Fe2B lamellar structure in the disproportionation step. The aspect ratio (A/R) of Fe2B structure increased from 3.37 ± 1.5 to 6.69 ± 3.2 during phase decomposition for 0 ~ 60 min at 820 ◦ C (P H2 = 10 kPa). The Fe2B having high A/R ratio recombined Nd2Fe14B, which is close to the single domain, and the magnetic properties are also improved with increasing A/R ratio.

Novel structures of TiC/TiAl2/carbon nanofiber (CNF) hybrid reinforcements with attached magnesium oxide (MgO) particles were successfully fabricated in the matrix of the Mg alloy AZ91 (Mg 9 wt%, Al 1 wt%, Zn) composite. This was done using a novel liquid pressing process, coupled with in situ reactions between titanium dioxide (TiO2)-coated CNFs and the Mg alloy. Homogeneously dispersed hybrid reinforcement with strong interfacial bonding through TiC/TiAl2, led to dramatic improvement in the mechanical properties of AZ91 alloys, with the assistance of an anchoring effect by MgO particles chemically attached to the coating layer.

Aluminum alloy (Al7075) composites reinforced with a high volume fraction of silicon carbide (SiC) were produced by a liquid-pressing process. The characterization of their microstructure showed that SiC particles corresponding to a volume fraction greater than 60% were uniformly distributed in the composite, and Mg2Si precipitates were present at the interface between the matrix and the reinforcement. A superior compressive strength (1130 MPa) was obtained by an effective load transfer to the hard ceramic particles. After solution heat treatment and artificial aging, the Mg2Si precipitates decomposed from rod-shaped large particles to smaller spherical particles, which led to an increase of the compressive strength by more than 200 MPa. The strengthening mechanism is discussed on the basis of the observed microstructural evolution.

Carbon-doped TiZrN nanocomposite coatings were investigated for phase formation and wear behavior. They were prepared by laser carburization using carbon paste, and the thermal energy of the pulsed laser was limited to the range of 20 to 50%. X-ray photoelectron spectroscopy analysis revealed that the ratio of carbide (TiC, ZrC) increased as the thermal energy of the laser increased. The sp2/sp3 ratio increased by approximately 16% when the laser thermal energy was raised from 30 to 40%, and the formation of amorphous carbon was confirmed in the carbon-doped TiZrN coatings. As a result of microstructural analysis, the carbon-doped TiZrN nanocomposite was formed by an increase of hybrid bonds in expanded localized carbon clusters. Wear resistance was evaluated using a ball-on-disc tester, which showed that the friction coefficient decreased from 0.74 to 0.11 and the wear rate decreased from 7.63 × 10−6 mm3 (Nm)−1 to 1.26 × 10−6 mm3 (Nm)−1. In particular, the friction coefficient and wear rate improved by 71 and 66%, respectively, owing to the formation of carbon-doped TiZrN nanocomposite with amorphous carbon while the thermal energy was increased from 30 to 40%.

In this study, different volume fractions of silicon-carbide-reinforced AA2024 matrix composites were successfully fabricated using stir-casting (SC) and die-casting (DC) processes. The microstructural difference and physical properties of the composites during the manufacturing process were investigated in detail. The microstructural analysis found that the composite produced by the SC process had some reinforcement clusters and pores, however, defects and clusters significantly decreased after the DC process. In particular, the degree of reinforcement dispersion was quantitatively analyzed and compared before and after the DC process using the dispersion-analysis method. As a result of quantitative evaluation, the degree of dispersion was improved 2.5, 4.6, and 4.0 times with 3 vol.%, 6 vol.%, and 9 vol.% SiC-reinforced composite after the DC process, respectively. The electron backscatter diffraction (EBSD) analysis showed that the grain size of the 9 vol.% SiC-reinforced DC composite (17.67 &mu, m) was 75% smaller than that of the SC composite (68.06 &mu, m). The average tensile strength and hardness of the 9 vol.% SiC-reinforced DC composite were 2 times higher than those of the AA2024 matrix. The superior mechanical properties of the DC-processed composite can be attributed to the increase in dispersivity of the SiC particles and to decreases in defects and grain size during the DC process.

Carbon-nanofiber (CNF) reinforced aluminum (Al) matrix composites were fabricated by a unique liquid pressing process. The mechanical properties of the CNF–Al composites, both with and without titanium dioxide (TiO 2 ) coating layers on the CNF surface, have been studied. The compressive yield strength of the TiO 2 coated CNF–Al composite dramatically increased (over nine times), as compared with that of an Al alloy. TiO 2 coated CNFs are expected to be a highly sustainable and dispersible reinforcement for metal matrix composites (MMCs) that are fabricated by a metal melting process.

This study was conducted on titanium diboride (TiB2) reinforced Al metal matrix composites (MMCs) with improved properties using a TiB2 and aluminum (Al) 1050 alloy. Al composites reinforced with fine TiB2 at volume ratios of more than 60% were successfully fabricated via the liquid pressing infiltration (LPI) process, which can be used to apply gas pressure at a high temperature. The microstructure of the TiB2&ndash, Al composite fabricated at 1000 &deg, C with pressurization of 10 bar for 1 h showed that molten Al effectively infiltrated into the high volume-fraction TiB2 preform due to the improved wettability and external gas pressurization. In addition, the interface of TiB2 and Al not only had no cracks or pores but also had no brittle intermetallic compounds. In conclusion, TiB2&ndash, Al composite, which has a sound microstructure without defects, has improved mechanical properties, such as hardness and strength, due to effective load transfer from the Al matrix to the fine TiB2 reinforcement.

High-temperature compressive strengths of titanium carbide (TiC) reinforced stainless steel composites fabricated by liquid pressing infiltration process were investigated at various temperatures. Effect of TiC on compressive strength of SUS431 was found to increase with increasing testing temperature. TiC reinforcement successfully suppressed softening of SUS431 matrix, resulting in about 5 times higher strength than that of SUS431 at 1050 °C. The novel SUS431 composites reinforced with uniformly dispersed, high volume fraction TiC show great promise for applications in high-temperature environments.

Interfacial characteristics and diffusion behavior of Ti 1− x Zr x N coatings under thermomechanical stress were investigated, in terms of morphologies and depth profiles, after pulsed laser ablation. TiZrN coatings were deposited on SUS304 substrates, using TiZr compound targets with Ti:Zr wt.% ratio of 90:10, 70:30, and 50:50. XRD patterns showed the same growth orientations of TiN and ZrN as (1 1 1), (2 0 0), and (2 2 0) in all coating specimens. The lattice parameters and the microhardness increased through solid solution with the substitutions of Zr to the Ti sites. Spalling of the coating layer was observed in the specimen of 10% wt.% Zr ratio after laser ablation. Delamination was suppressed as the substitution of Zr increased, and it could be attributed to the formation of ZrN which can promote heat transfer in the coating layer faster than TiN. SIMS depth profiles revealed that the diffusion distance of the coating (Ti, Zr) and the substrate (Cr, Fe) atoms decreased, due to diffusion path reduction by the solid solution effects.

Aluminum-silicon-based and zinc-based metallic coatings have been widely used for hot-stamped boron steel in automotive applications. In this study, resistance spot weldability was explored by investigating the effects of the properties of metallic coating layers on heat development and nugget growth during resistance spot welding. In the case of the aluminum-silicon-coated hot-stamped boron steel, the intermetallic coating transformed into a liquid film that covered the faying interface. A wide, weldable current range was obtained with slow heat development because of low contact resistance and large current passage. In the case of the zinc-coated hot-stamped boron steel, a buildup of liquid and vapor formation under large vapor pressure was observed at the faying interface because of the high contact resistance and low vaporization temperature of the intermetallic layers. With rapid heat development, the current passage was narrow because of the limited continuous layer at the faying interface. A more significant change in nugget growth was observed in the zinccoated hot-stamped boron steel than in the aluminum-silicon-coated hot-stamped boron steel.

The degradation behavior of TiN coatings on Inconel 617 and silicon (Si) wafer substrates was compared following Nd:YAG pulsed laser ablation to apply thermomechanical stress. Surface cracks and pores were observed on the TiN coating on the Inconel 617 after five pulses, and melting of the coating was occurred over ten pulses. The TiN coating on the Si wafer also showed surface cracks and pores, but there was no surface melting. As the pulses were increased, the surface roughness of the TiN coating on Inconel 617 increased more than the TiN coating on the Si wafer, and interfacial cracking was the dominant degradation behavior on the Si wafer. The hardness of the TiN coating decreased below 50% of its initial value (2200 HK) after five pulses on the Inconel 617, whereas over 70% of the initial value (2400 HK) was maintained on the Si wafer. The TiN coating on Inconel 617 showed diffusion of substrate atoms to the surface, while Si was not found in the TiN coating on the Si wafer even after 25 pulses. It was determined that the decrease in hardness was influenced by the cracking behavior and the diffusion of atoms from the substrate.