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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Effects of Overlapping Distances on Steel Microstructure and Properties After Multi-track Laser Quenching

In this study, multi-track laser quenching with different overlapping distances was used to assess SM45C microstructure and properties. Two overlapping distance types were evaluated, including overlapping distances in the transition and martensite regions, respectively. After multi-track quenching, hardness showed a threefold increase. With the overlapping distance in the transition region, surface hardness varied from 600 to 700 HV. There was a region of low hardness in each track. Hardness in the low hardness region was from 300 to 400 HV. The average hardness was basically over 500 HV with the overlapping distance in the martensite region, although there was a softening region. The increased hardness was mainly caused by the martensite. Microstructure in the overlapping region was self-tempered martensite, retained austenite and ferrite. Tempered sorbite and lowly tempered martensite were observed in heat-affected zones. Friction coefficients of quenched specimens varied between 0.275 and 0.325, with a 14% reduction relative to the base metal. The wear rate of the quenched specimen was only 40.8% of the base metal. With time, mass reduction in the quenched specimen was much smaller than that of the base metal. For specimens treated with laser quenching, slight fatigue wear was dominating.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A Modified Isotropic–Kinematic Hardening Model to Predict the Defects in Tube Hydroforming Process

Numerical simulations of tube hydroforming process of hollow crankshafts were conducted by using finite element analysis method. Moreover, the modified model involving the integration of isotropic–kinematic hardening model with ductile criteria model was used to more accurately optimize the process parameters such as internal pressure, feed distance and friction coefficient. Subsequently, hydroforming experiments were performed based on the simulation results. The comparison between experimental and simulation results indicated that the prediction of tube deformation, crack and wrinkle was quite accurate for the tube hydroforming process. Finally, hollow crankshafts with high thickness uniformity were obtained and the thickness distribution between numerical and experimental results was well consistent.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effects of Heat Treatment on Corrosion and Wear Behaviors of Mg-6Gd-2Zn-0.4Zr Alloy in Simulated Body Fluid

Mg-6Gd-2Zn-0.4Zr (wt.%, GZ62K) alloy was processed by solution treatment under different temperatures. The microstructure, hardness, corrosion and wear behaviors in simulated body fluid (SBF) have been studied. The results indicate that the (Mg, Zn){sub 3}Gd phase decreases, the precipitated phases gradually increase, and the long-period stacking ordered structure disappears with the increase of solution temperature. The alloy has better corrosion resistance after solution treatment, and that solution treated at 490 °C for 12 h shows the best corrosion resistance. The friction coefficient of the alloy under dry sliding condition decreases slightly, but the mass loss increases with increasing the solution temperature. The alloy solution treated at 460 °C for 12 h exhibits the lowest friction coefficient and mass loss in SBF, and it also has the best wear resistance under dry sliding condition.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of MoSi{sub 2} Content on Dry Sliding Tribological Properties of Zr-Based Bulk Metallic Glass Composites

Zr{sub 55}Cu{sub 30}Al{sub 10}Ni{sub 5} bulk metallic glass and its composites were prepared by suction casting into a copper mold. The effect of MoSi{sub 2} content on the tribological behavior of Zr{sub 55}Cu{sub 30}Al{sub 10}Ni{sub 5} BMG was studied by using a high-speed reciprocating friction and wear tester. The results indicate that the friction coefficient and wear resistance of the BMGs can be improved by a certain amount of crystalline phase induced by MoSi{sub 2} content from 1 to 3% and deteriorated with MoSi{sub 2} content of 4%. The wear mechanism of both the metallic glass and its composite is abrasive wear. The mechanism of crystalline phase-dependent tribological properties of the composite was discussed based on the wear track and mechanical properties in the present work. The wear behavior of Zr{sub 55}Cu{sub 30}Al{sub 10}Ni{sub 5} BMG and its composite indicates that a good combination of the toughness and the hardness can make the composite be well wear resistant.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Relationship Between the Integrity of Lubricating Film and the Tribological Behavior on TiAl-Ag Self-Lubricating Composites

To explore the relationship between the integrity of the lubricating film and the tribological behavior of a metal matrix self-lubricating composite, the friction and wear experiments of TiAl-Ag self-lubricating composites were carried out with a ball-on-disk configuration. Besides, an approximate model was developed for analyzing the relationship based on Blau’s theory. The research results suggest that the friction and wear behavior of the TiAl-Ag self-lubricating composites changes in accordance with the formation conditions of the Ag-rich lubricating film. Specifically, the friction coefficients and wear rates of the TiAl-Ag self-lubricating composites decreased from high levels at full composite–counterface ball contact to low levels at full-film lubrication. Hence, the integrity of the lubricating film is a possible criterion for the self-lubricating property of the self-lubricating composites.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Tribological Properties of NiAl Matrix Composites Filled with Serpentine Powders

The unexplored tribological properties of NiAl matrix composites filled with serpentine powders are investigated using a reciprocating ball-on-disk configuration. Tribological test results reveal that increasing the serpentine concentration to some extent reduces the friction coefficients and wear rates of the composites. The best anti-friction and anti-wear performance is displayed by the NiAl matrix composite filled with 8 wt.% serpentine and 2 wt.% TiC (NAST). Microstructural analyses demonstrate that after adding serpentine, the self-lubricating films with different percentages of coverage form on the worn surfaces of the composites. A self-lubricating film with the highest percentage of coverage smears on the worn surface of NAST. This clearly suggests that serpentine can act as a new type of filler for NiAl matrix composites, whereas a combination of serpentine and TiC can enable serpentine to provide a full play to its excellent lubricating performance.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Coil Current on the Properties of Hydrogenated DLC Coatings Fabricated by Filtered Cathodic Vacuum Arc Technique

We successfully prepared hydrogenated DLC (a-C:H) with a thickness higher than 25 μm on stainless steel using a filtered cathode vacuum arc (FCVA) technique. The structural and mechanical properties of DLC were systematically analyzed using different methods such as x-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, Vickers hardness, nanohardness, and friction and wear tests. The effect of coil current on the arc voltage, ion current, and mechanical properties of resultant films was systematically investigated. The novelty of this study is the fabrication of DLC with Vickers hardness higher than 1500 HV, in the meanwhile with the thickness higher than 30 μm through varying the coil current with FCVA technique. The results indicated that the ion current, deposition rate, friction coefficient, and Vickers hardness of DLC were significantly affected by the magnetic field inside the filtered duct.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Tribological Performance of Ni{sub 3}Al Matrix Self-Lubricating Composites Containing Multilayer Graphene Prepared by Additive Manufacturing

In order to improve tribological performance of Ni{sub 3}Al-based alloy, Ni{sub 3}Al matrix composites containing 1.5 wt.% multilayer graphene (MLG) are prepared through additive manufacturing (AM) and spark plasma sintering (SPS), which are denoted as NMAM and NMSPS, respectively. Tribological behaviors of NMAM and NMSPS against Si{sub 3}N{sub 4} balls are researched under constant speed (0.2 m/s) and varied loads (from 4 to 16 N) for evaluating the tribological properties of NMAM and NMSPS. The results present that NMAM exhibits the excellent tribological properties [low friction coefficients (0.26-0.40) and considerable wear resistance (2.8-4.6 × 10{sup −5} mm{sup 3} N{sup −1} m{sup −1})] as compared to NMSPS, which attributes to the uniform enrichment of MLG with properties of high tensile strength and being easily sheared off on the worn surfaces. Owing to the use of spherical prealloyed powder containing multilayer graphene and the characteristics of layer by layer depositing in the AM process, NMAM has a more compact and uniform substrate, which persistently provides a source of the formation of continuous and stable frictional layer. Due to the characteristics of AM rapid solidification, NMAM has the small grain size and well-compacted microstructure, which can effectively reduce the probability of spalling wear and lead to the increase in wear resistance of materials. The research can offer the reference for self-lubricating materials prepared by AM technology.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Applied Load and Sliding Speed on Tribological Behavior of TiAl-Based Self-Lubricating Composites

This article was dedicated to explore the combined lubrication of silver, MoS{sub 2} and carbon nanotubes (CNTs) based on the changes in applied loads and sliding speeds. The results showed that the formed lubricating films played the major role in undertaking the equivalent stress, as well as effectively reduced friction resistance and material loss. It led to small friction coefficient and less wear rate at 1.2 m/s. At 1.2 m/s-16 N, an integrated lubricating film containing Ag, CNTs and MoS{sub 2} was continuously formed, which well provided the excellent lubricating property, resulting in lower friction coefficient (0.19) and less wear rate (1.56 × 10{sup −5} mm{sup 3}/N m). The formation of Ag and CNTs enriched islands acted as the bearing areas and played the major role in resisting friction resistance. Meanwhile, solid lubricant MoS{sub 2} was enriched in the lubricating film and effectively protected lubricating film from being destroyed, resulting in small friction coefficient and less wear rate at 1.2 m/s-16 N.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

The Sliding Wear and Friction Behavior of M50-Graphene Self-Lubricating Composites Prepared by Laser Additive Manufacturing at Elevated Temperature

M50 steel is widely applied to manufacture aircraft bearings where service lives are mainly determined by the friction and wear behaviors. The main purpose of this study is to investigate the tribological behaviors and wear mechanisms of M50-1.5 wt.% graphene composites (MGC) prepared by laser additive manufacturing (LAM) (MGC-LAM) sliding against Si{sub 3}N{sub 4} ball from 25 to 550 °C at 18 N–0.2 m/s. XRD, EPMA, FESEM, and EDS mapping were conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MGC-LAM. The results indicated that MGC-LAM showed the excellent friction and wear performance at 25-550 °C for the lower friction coefficient of 0.16-0.52 and less wear rate of 6.1-9.5 × 10{sup −7} mm{sup 3} N{sup −1} m{sup −1}. Especially at 350 °C, MGC-LAM obtained the best tribological performance (0.16, 6.1 × 10{sup −7}mm{sup 3} N{sup −1} m{sup −1}). It was attributed to the dense coral-like microstructure, as well as the formed surface lubricating structure which is composed of the upper uniform lubricating film with massive graphene and the underneath compacted layer.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Surface Modification of C17200 Copper-Beryllium Alloy by Plasma Nitriding of Cu-Ti Gradient Film

In the present work, a copper-titanium film of gradient composition was firstly fabricated by the dual magnetron sputtering through power control and plasma nitriding of the film was then conducted to modify C17200 Cu alloy. The results showed that the prepared gradient Cu-Ti film by magnetron sputtering was amorphous. After plasma nitriding at 650 °C, crystalline Cu-Ti intermetallics appeared in the multi-phase coating, including CuTi{sub 2}, Cu{sub 3}Ti, Cu{sub 3}Ti{sub 2} and CuTi. Moreover, even though the plasma nitriding duration of the gradient Cu-Ti film was only 0.5 h, the mechanical properties of the modified Cu surface were obviously improved, with the surface hardness enhanced to be 417 HV{sub 0.01}, the wear rate to be 0.32 × 10{sup −14} m{sup 3}/Nm and the friction coefficient to be 0.075 at the load of 10 N, which are all more excellent than the C17200 Cu alloy. In addition, the wear mechanism also changed from adhesion wear for C17200 Cu substrate to abrasive wear for the modified surface.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Determination of the Frictional Behavior at Compaction of Powder Materials Consisting of Spray-Dried Granules

The frictional behavior during powder compaction and ejection is studied using an instrumented die with eight radial sensors. The average friction over the total powder pillar is used to determine a local friction coefficient at each sensor. By comparing forces at compaction with forces at ejection, it can be shown that the Coulomb’s friction coefficient can be described as a function of normal pressure. Also stick phenomena has been investigated in order to assess its influence on the determination of the local friction coefficient.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Surface Texturing of Polyimide Composite by Micro-Ultrasonic Machining

In this study, micro-dimples were prepared on a polyimide composite surface to obtain the dual benefits of polymer materials and surface texture. Micro-ultrasonic machining is employed for the first time for micro-dimple fabrication on polyimide composite surfaces. Surface textures of simple patterns were fabricated successfully with dimple depths of 150 μm, side lengths of 225-425 μm, and area ratios of 10-30%. The friction coefficient of the micro-dimple surfaces with side lengths of 325 or 425 μm could be increased by up to 100% of that of non-textured surfaces, alongside a significant enhancement of wear resistance. The results show that surface texturing of polyimide composite can be applied successfully to increase the friction coefficient and reduce wear, thereby contributing to a large output torque.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Improvement of Tribological Performance of AISI H13 Steel by Means of a Self-Lubricated Oxide-Containing Tribo-layer

A self-lubricated oxide-containing tribo-layer was induced to form by continuously adding particles of MoS{sub 2}, Fe{sub 2}O{sub 3} or their mixtures onto sliding interfaces of AISI H13 and 52100 steels. The artificial tribo-layer was always noticed to form continuously and cover the worn surface (termed as cover-type), whereas the original tribo-layer spontaneously formed with no additive was usually discontinuous and inserted into the substrate (termed as insert-type). Clearly, the cover-type and insert-type tribo-layers exactly corresponded to low and high wear rates, respectively. For the mixed additives of Fe{sub 2}O{sub 3} + MoS{sub 2}, the protective tribo-layers presented a load-carrying capability and lubricative function, which are attributed to the existence of Fe{sub 2}O{sub 3} and MoS{sub 2}. Hence, the wear rates and friction coefficients of H13 steel were markedly reduced.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Electropulsing-Assisted Ultrasonic Nanocrystalline Surface Modification on the Surface Mechanical Properties and Microstructure of Ti-6Al-4V Alloy

The effect of electropulsing-assisted ultrasonic nanocrystalline surface modification (EP-UNSM) on surface mechanical properties and microstructure of Ti-6Al-4V alloy is investigated. Compared to conventional ultrasonic nanocrystalline surface modification (UNSM), EP-UNSM can effectively facilitate surface roughness and morphology, leading to excellent surface roughness (reduced from Ra 0.918 to Ra 0.028 μm by UNSM and Ra 0.019 μm by EP-UNSM) and smoother morphology with less cracks and defects. Surface friction coefficients are enhanced, resulting in lower and smoother friction coefficients. In addition, the surface-strengthened layer and ultra-refined grains are significantly enhanced with more severe plastic deformation and a greater surface hardness (a maximum hardness value of 407 HV and an effective depth of 550 μm, in comparison with the maximum hardness value of 364 HV and effective depth of 300 μm obtained by conventional UNSM). Remarkable enhancement of surface mechanical properties can be attributed to the refined gradient microstructure and the enhanced severe plastic deformation layer induced by coupling the effects of UNSM and electropulsing. The accelerated dislocation mobility and atom diffusion caused by the thermal and athermal effects of electropulsing treatment may be the primary intrinsic reasons for these improvements.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation on Tribological Properties of the Pre-oxidized Ti{sub 2}AlN/TiAl Composite

Different oxidation layers on the Ti{sub 2}AlN/TiAl substrate which was fabricated by in situ synthesis were prepared through thermal oxidation process. The microstructure, phase identification and elements distribution of the oxidation layers were analyzed. The tribological performance of pre-oxidized composites against Si{sub 3}N{sub 4} ball at 25 and 600 °C, as well as the effect of pre-oxidation layers on tribological performance was systematically investigated. The results show that, compared to Ti{sub 2}AlN/TiAl, the pre-oxidized composites present more excellent tribological properties, especially the wear resistance at 600 °C. It is a significant finding that, different from severe abrasive wear and plastic deformation of Ti{sub 2}AlN/TiAl, the tribo-films formed by the pre-oxidation layers on the worn surface of pre-oxidized composites weaken abrasive wear and suppress the development of plastic deformation to protect the underlying composite substrate from wear. Moreover, the stable cooperation on the interface between tribo-films and Si{sub 3}N{sub 4} ball results in the relatively steady friction coefficient.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mechanical Properties and Wear Behavior of AA5182/WC Nanocomposite Fabricated by Friction Stir Welding at Different Tool Traverse Speeds

Grain growth inhibition at the heat-affected zone, improved weld strength and superior tribological properties of welds are desirable attributes of modern manufacturing. With the focused on these attributes, tungsten carbide (WC) nanoparticles were employed as reinforcements for the friction stir welding of 5-mm-thick AA5182 aluminum alloy by varying tool traverse speeds. The microstructure, microhardness, ultimate tensile strength, fracture and wear behavior of the resultant WC-reinforced welds were investigated, while unreinforced AA5182 welds were employed as controls for the study. The result shows that the addition of WC nanoparticles causes substantial grain refinement within the weld nugget. A decrease in traverse speed caused additional particle fragmentation, improved hardness value and enhanced weld strength in the reinforced welds. Improved wear rate and friction coefficient of welds were attained at a reduced traverse speed of 100 mm/min in the WC-reinforced welds. This improvement is attributed to the effects of reduced grain size/grain fragmentation and homogeneous dispersion of WC nanoparticles within the WC-reinforced weld nugget.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructures and Properties of Nanostructured TiN/MoS{sub 2}/Ag Composite Film Prepared by Pulsed Laser Deposition

In this work, the structural and mechanical properties, tribological performance, and lubrication mechanism from room temperature to 900 °C of TiN/MoS{sub 2}/Ag composite films were investigated in detail. Nanostructured TiN/MoS{sub 2}/Ag composite film was obtained by assembling targets using pulsed laser deposition. The incorporation of lubricant layered MoS{sub 2} and soft metal Ag led to degraded mechanical properties, which could contribute to the lower friction coefficients at low temperatures. When the temperature increased to above 500 °C, the generated high-temperature lubricant MoO{sub 3} and silver molybdates played a critical synergetic lubrication effect, which formed a layer of lubricating film and reduced the friction coefficient. Thus, the cooperation of various lubrication phases contributed to improvement of tribological performance and resulted in continuous lubrication from room temperature to 900 °C.

77 NANOSCIENCE AND NANOTECHNOLOGY↗