Characteristics of powder metallurgy pure titanium matrix composite reinforced with multi-wall carbon nanotubes

Abstract

By using pure titanium powder coated with un-bundled multi-wall 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 157 MPa and 169 MPa, respectively, compared to those of extruded titanium materials with no CNT additive. 2Fractured 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.

High-temperature properties of extruded titanium composites fabricated from carbon nanotubes coated titanium powder by spark plasma sintering and hot extrusion

“…Unfortunately, the exact strengthening mechanism by the remained CNTs in the Ti composites at room and elevated temperatures is still unclear because the exact amount of CNTs transformed to TiC is unknown. However, the remained CNTs are expected to improve the mechanical properties which are consistent with the previous report [10,[13][14][15].…”

“…4. The improvement of mechanical properties, in particular yield stress, of the composites at room temperature can be considered that due to the effect of grain size, solid solution of carbon and TiC second phase including the remained CNTs [10,14]. The strengthening mechanism due to grain size effect was estimated by Hall-Petch relationship [23][24] using the material constants in Ref.…”

“…Ti and its alloys are also interested as competitive matrix materials because they exhibit high specific strength which is an important factor for weight reduction of the airplane and automotive applications from the viewpoint of energy consumption. The previous work [14] has demonstrated a successful improvement of tensile properties at room temperature of the commercially pure Ti reinforced with CNTs via wet processing in powder metallurgy route. However, the improvement of mechanical properties of commercially pure Ti at elevated temperature is also important because some applications need to use or exposure to high temperature such as exhaust system of airplanes, automotives and power plants [17][18].…”

“…Recently, CNTs have been widely used as reinforcing materials for metal matrix composites (MMCs). The previous studies indicated the remarkable characteristics of MMCs reinforced with CNTs, such as aluminium [5][6][7], magnesium [8][9][10], copper [11][12] and titanium [13][14][15][16]. Ti and its alloys are also interested as competitive matrix materials because they exhibit high specific strength which is an important factor for weight reduction of the airplane and automotive applications from the viewpoint of energy consumption.…”

“…The solid zwitterionic substances were solidified as thin film solids and existed on the Ti surface during drying process. Those thin film solids needed to be eliminated before consolidation because they were changed to gases at temperature of above 773 K [14], resulting in pore defects in the consolidated bulk materials. The coated Ti powders were heated again in a horizontal tube furnace at 873 K for 3.6 ks under a protective Ar gas.…”