Junko Umeda

CNTs/TiC reinforced titanium matrix nanocomposites via powder metallurgy and its microstructural and mechanical properties

By using pure titanium powder coated with unbundled multiwall carbon nanotubes (MWCNTs) via wet process, powder metallurgy (P/M) titanium matrix composite (TMC) reinforced with the CNTs was prepared by spark plasma sintering (SPS) and subsequently hot extrusion process. The microstructure and mechanical properties of P/M pure titanium and reinforced with CNTs were evaluated. The distribution of CNTs and in situ formed titanium carbide (TiC) compounds during sintering was investigated by optical and scanning electron microscopy (SEM) equipped with EDS analyzer. The mechanical properties of TMC were significantly improved by the additive of CNTs. For example, when employing the pure titanium composite powder coated with CNTs of 0.35 mass%, the increase of tensile strength and yield stress of the extruded TMC was 157MPa and 169MPa, respectively, compared to those of extruded titanium materials with no CNT additive. Fractured surfaces of tensile specimens were analyzed by SEM, and the uniform distribution of CNTs and TiC particles, being effective for the dispersion strengthening, at the surface of the TMC were obviously observed.

Inter-wall bridging induced peeling of multi-walled carbon nanotubes during tensile failure in aluminum matrix composites.

In situ scanning electron microscopy (SEM) observation of a tensile test was performed to investigate the fracturing behavior of multi-walled carbon nanotubes (MWCNTs) in powder metallurgy Al matrix composites. A multiple peeling phenomenon during MWCNT fracturing was clearly observed. Its formation mechanism and resultant effect on the composite strength were examined. Through transition electron microscopy characterizations, it was observed that defective structures like inter-wall bridges cross-linked adjacent walls of MWCNTs. This structure was helpful to improve the inter-wall bonding conditions, leading to the effective load transfer between walls and resultant peeling behaviors of MWCNTs. These results might provide new understandings of the fracturing mechanisms of carbon nanotube reinforcements for designing high-performance nanocomposites.

Strengthening behaviour and mechanisms of extruded powder metallurgy pure Ti materials reinforced with ubiquitous light elements

Ubiquitous light elements (ULEs) like oxygen (O), nitrogen (N), carbon (C) and hydrogen (H) can be the key additive elements to achieve the high specific strength and cost-effectiveness of powder metallurgy (PM) titanium (Ti) materials. They have high potential to be employed as promising useful reinforcements of conventional expensive alloying elements like vanadium (V) and Niobium (Nb). In this study, two ULEs, oxygen and hydrogen, were induced into pure Ti matrix via the PM route, and then the processed Ti powders were consolidated into the extruded Ti–O–H materials. The additive ULEs’ contribution to the microstructures and strengthening behaviour of Ti wrought materials was investigated in detail. The extruded Ti–0.97O–0.11H specimen exhibited an excellent combination of ultimate tensile strength (UTS) of 1158 MPa and tensile elongation of 23.9%, which were superior to those of Ti–6Al–4V alloy (UTS: 1047 MPa, elongation: 16.6%).

Microstructural and Mechanical Properties of Titanium Matrix Composites Reinforced with Nano Carbon Materials via Powder Metallurgy Process

Powder metallurgy (P/M) titanium matrix composite (TMC) reinforced with multi-wall carbon nanotube (MWCNT) was prepared by spark plasma sintering (SPS) and hot extrusion process, where the powder surface was coated by un-bundled CNTs via wet process. The microstructure and mechanical properties of P/M pure titanium and reinforced with CNTs were evaluated. The distribution of CNTs and in-situ formed titanium carbide (TiC) compounds during sintering was investigated by optical and scanning electron microscopy (SEM) equipped with EDS analyser. The mechanical properties of TMC were significantly improved by adding a small amount of CNTs. For example, when employing the pure titanium composite powder coated with CNTs of 0.35 mass%, the increase of tensile strength and yield stress of the extruded TMC was 157 MPa and 169 MPa, respectively, compared to those of extruded titanium materials with no CNT additive. Fractured surfaces of specimens were analysed by SEM, and the uniform distribution of CNTs and TiC particles, being effective for the dispersion strengthening, at the surface of the TMC were obviously observed.

Machinable Cu-40%Zn Composites Containing Graphite Particles by Powder Metallurgy Process

Advanced Cu-40mass%Zn alloys with a high tensile strength and excellent machinability have been developed via a powder metallurgy (P/M) process. They are environmentally benign because fine graphite particles are included instead of lead (Pb) to improve their machinability. The effect of the content and particle size of the graphite on the mechanical properties and machinability are investigated in this paper. When applying a conventional P/M process consisting of the cold compaction and hot extrusion to consolidate elementally premixed mixture of Cu-40mass%Zn and graphite powder, the addition of 1 mass% graphite particles with 5∼10 𝜇m in diameter is suitable to obtain a high tensile strength and good machinability at the same time.

Estimation of Compositions of Zr-Cu Binary Sputtered Film and Its Characterization

Zr-Cu amorphous films were prepared by radio-frequency (RF) magnetron sputtering on glass substrate using two kinds of the elemental composite targets: Cu chips on Zr plate and Zr chips on Cu plate. It was easy to precisely control chemical compositions of sputtered films by selecting the chip metal and the number of chips. It is possible to accurately estimate the film compositions by using the sputtered area and the deposition rate of Cu and Zr. XRD analysis on every as-sputtered film showed the broadened pattern. Zr-rich composition film, however, revealed a small peak at the diffraction angle of 2𝜃=35∘, and Cu-rich one indicated it at 2𝜃=43∘. TEM and electron diffraction analysis on the former also showed the main Zr ring patterns and its streaks. Zr-rich composition film with Cu content of 34 at% or less indicated a good corrosion resistance by salt spray test. On the other hand, Cu-rich version with 74 at% Cu or more was poor in corrosion resistance. This was because Zr was reactively passive, and caused the spontaneous formation of a hard non-reactive surface film that inhibited further corrosion than Cu.

The Development of a Ti-6Al-4V Alloy via Oxygen Solid Solution Strengthening for Aerospace and Defense Applications

The high cost of titanium has historically prevented widespread use in military ground vehicles. Two strategies to make this material more cost effective and viable are to reduce the cost of titanium armors or to improve the ballistic performance of titanium and reduce the amount of material required. This paper investigates the latter strategy. Mixtures of titanium powders and TiO2 particles were employed as starting materials and consolidated by spark plasma sintering (SPS) and hot extrusion. The content of TiO2 particles was 0~1.5% of the mass mixture. Solidification of oxygen atoms (from TiO2 particles) into Ti matrix occurred at 1073K for 1800 seconds in a vacuum. Tensile testing showed that Tensile Strength (TS) and Yield Strength (YS) increased in proportion to TiO2 content but elongation decreased slightly with increased TiO2 content. Extruded pure Ti powder material with 1.5% TiO2 particles produced 1040 MPa TS, 902 MPa YS and 25.1% elongation when tested. When using Ti-6Al-4V (Ti-64) alloy powders with 0.5% TiO2 particles, the final extruded Ti-64 powder bars with oxygen solid solution showed 1226 MPa TS and 22.7% elongation. Initial ballistic evaluation showed the Ti-64 powder bars with 0.5% TiO2 particles yielded a marked improvement over the conventionally rolled Ti-64 alloy plate.

The In Situ Fabrication of Al-AlN Composites from Metal Powders and their Resistance to Wear and Cavitation

Recent breakthroughs in the sintering of aluminium alloys under nitrogen have opened the way for the in-situ fabrication of Al-AlN composites in a controllable and reproducible fashion over a wide range of volume fractions of AlN. This work reviews the fundamentals for the in-situ fabrication of the Al-AlN composites from metal powders and highlights their technical potential for niche applications because of their excellent resistance to cavitation erosion in water and their unusually low friction coefficient under oil lubrication.

Tribological Analysis of Particulates Reinforced Powder Metallurgy Magnesium Alloy Composites under Oil Lubrication Condition

For the evaluation of wear behavior of Mg composites under oil lubrication conditions, powder metallurgy alloy reinforced with additive particles were fabricated by the repeated plastic working (RPW) and hot extrusion. The RPW process was effective in refining both reinforcements and -Mg grains causing the matrix hardening. When increasing the repetition number of RPW process from 200 to 600 cycles, the particle size of additives changed from 8 m to 1~2 m, and -Mg grain size was 1 m or less. With regard to the defensive and offensive properties of Mg alloys reinforced with dispersoids, the composite had superior adhesive wear resistance compared with the conventional Mg alloys because of its extremely high microhardness of 95~180 Hv by RPW process. The uniform distribution of refined particles was useful for improving both defensive and offensive properties against AZ31B counter disk specimens. The prominent dispersoids in the matrix were also effective in forming the oil grooves around them, and caused the low and stable friction coefficient. On the other hand, in the case of the composite containing coarse particles, severely deep scratches were given on the counter face of the AZ31B disk, and resulted in an unstable and high friction coefficient.

Effect of initial state on dispersion evolution of carbon nanotubes in aluminium matrix composites during a high-energy ball milling process

In this study, a pre-mixing process was applied to assist a high-energy ball milling (HEBM) process to fabricate high-strength aluminium (Al) matrix composites reinforced with carbon nanotubes (CNTs) by powder metallurgy. Effects of initial state on the dispersion quality of CNTs in composites and resultant mechanical properties were investigated using electron microscopy and tensile testing, respectively. Results showed that after pre-mixing, raw CNT agglomerations became flattened CNT clusters, and evolved into individually dispersed CNT fragments on flaky Al powder surface after HEBM for 12 h. However, CNT clusters remained in the same HEBM process without pre-mixing. Both individual CNTs and CNT clusters were observed inside cold-welded Al particles with a prolonged milling time of 24 h. By applying pre-mixing, the reinforcing effect in CNT/Al composites increased by more than 100%. The distinct evolution processes of CNT dispersion during HEBM with different initial states have been discussed.