Mechanical Behavior of W-Y2O3 and W-Ti Alloys from 25 °C to 1000 °C

Abstract

The mechanical behavior of pure W, W-0.5 wt pct Y 2 O 3 , and W-4 wt pct Ti manufactured by powder metallurgy was studied from ambient temperature to 1000°C. Y 2 O 3 nanoparticles were added to inhibit grain growth and improve oxidation resistance, while Ti is a sintering activator. Strength and toughness were measured from the three-point bend tests in smooth and notched prismatic bars. The dominant deformation and failure micromechanisms were assessed as a function of temperature for each material through the analysis of the fracture surfaces and transverse cross sections in the scanning electron microscope. In particular, the role played by microstructure, dominant failure mechanisms, and oxidation rates in mechanical behavior were elucidated for each material in the entire temperature range. It was found that Y 2 O 3 improved the high-temperature properties by inhibiting oxidation. The Ti acted as a sintering activator, and the W-Ti alloy was fully dense and presented smaller grain size. Both factors enhanced the mechanical properties at ambient and intermediate temperatures, but the ductile-to-brittle transition temperature (DBTT) of this material was higher, leading to brittle behavior up to very high temperature.

Mechanical properties of Y2O3-doped W–Ti alloys

“…The values of the Vickers hardness for both alloys are shown in Table 1, which also includes the data in [20] and [17] for W and fully dense W 4Ti, respectively, processed following the same route. The hardness values for pure W are similar to those reported in [21] for sintered W with densities in the range 87 92%.…”

“…The bonding between sintered W and WL10 appears to be success fully accomplished using a Ti interlayer [18]. The mechanical behavior of W 4%Ti in the range 25 1000 °C has been reported else where [17]. This alloy exhibited enhanced strength and brittle behavior up to 1000 °C.…”

“…A Y 2 O 3 dispersion, apart from strengthening the matrix and inhibiting grain growth, enhances oxidation resistance. In particular, it has been found that 0.5 wt.% Y 2 O 3 addition remarkably enhances the oxidation resis tance of PM W [17,19] with sizes between 10 nm and 50 nm. The powder blends with the target compositions were milled inside a WC vessel sealed under a high purity Ar atmo sphere, for 2 h in a high energy planetary mill using WC balls of 10 mm in diameter as grinding media.…”

“…For instance, it has been shown that La 2 O 3 dispersion or Al K Si doping can signifi cantly improve the mechanical strength and the RCT of W, but it appears that the DBTT cannot be lowered this way [6,12 14]. Y 2 O 3 additions strengthen W and increase its creep resistance [15,16] and it has recently been reported that Y 2 O 3 doped W pro duced by powder metallurgy (PM) and consolidated by hot iso static pressing (HIP) achieves certain ductility at 400 °C [17]. In addition, this Y 2 O 3 doped W presented enhanced mechanical properties and a remarkable oxidation resistance at high tempera tures, in comparison to W produced by the same procedure [17].…”

La2O3-reinforced W and W–V alloys produced by hot isostatic pressing

“…Recently, W and W Ti alloys reinforced with Y 2 O 3 have been sintered by HIP [12]. The use of Ti as sintering acti vator and the Y 2 O 3 dispersion result in full dense materials exhib iting improved mechanical properties and oxidation resistance [13]. However, the Y 2 O 3 particles in a W matrix appear to be unsta ble at temperatures above 1600 K becoming into coarse particles of complex W Y and W Y Ti oxides, which could worsen the mechanical properties.…”