Excellent Room-temperature Mechanical Properties Research Articles

Laser powder bed fusion to fabricate high-entropy alloy FeCoCrNiMo0.5 with excellent high-temperature strength and ductility

FeCoCrNi, a high-entropy alloy fabricated by laser powder bed fusion, has excellent room-temperature mechanical properties but poor high-temperature mechanical performance. To expand the application of FeCoCrNi, in this study, we added Mo to form σ precipitates, which improved the high-temperature mechanical properties of the alloy via Orowan strengthening. We also elucidated the main deformation mechanism of FeCoCrNiMo0.5, involving the transformation of the deformational mode from dislocation-based motion to twinning deformation.

Design and development of a high-performance Ni-based superalloy WSU 150 for additive manufacturing

This research proposes a design and development strategy of a new nickel-based superalloy for additive manufacturing. A new Ni-based superalloy has been developed by the application of the combinatorial alloy development technique coupled with CALPHAD based solidification modeling by effectively suppressing the precipitation kinetics. The suppression of precipitation during processing paved a way for prevention of cracks during deposition. The new alloy “WSU 150″ revealed excellent room temperature mechanical properties with a yield strength of 867 MPa, an ultimate tensile strength of 1188 MPa, and an elongation of 27.9% in the as-deposited condition. The mechanical properties of the heat-treated alloy were improved significantly to 1114 MPa yield strength, 1396 MPa ultimate tensile strength, and an elongation of 16.1%. Improvement in the mechanical properties is attributed to the additional precipitation and coarsening of γʹ and carbides during heat-treatment. Microstructural investigation of the alloy revealed spherical γʹ with a rippled size distribution from the center to the interdendritic region. The average size of the γʹ particles in the as-deposited condition was found to be around 48 nm in the interdendritic region. Heat-treatment promoted the coarsening of γʹ which is explained in the paper.

The Dry Sliding Wear Properties of Nano-Sized TiCp/Al-Cu Composites at Elevated Temperatures.

Nano-sized ceramic particle reinforced aluminum composites exhibit excellent room-temperature mechanical properties. However, there is limited research on the dry sliding wear behavior of those composites at elevated temperatures, which should be one of the major concerns on elevated temperature applications. Here the Al-Cu composites reinforced with nano-sized TiCp were fabricated. The dry sliding wear behaviors of the nano-sized TiCp/Al-Cu composites at various temperatures (140–220 °C) and loads (10–40 N) with different TiCp contents were studied, and the results showed that the nanocomposites exhibited superior wear resistance. For instance, the relative wear resistance of the 0.5 wt.% nano-sized TiCp/Al-Cu composite was 83.5% higher than that of the Al-Cu matrix alloy at 180 °C under 20 N, and was also 16.5% higher than that of the 5 wt.% micro-sized TiCp/Al-Cu composite, attributed to the pronounced Orowan strengthening effect of nanoparticles. The wear rates of the nanocomposites were always lower than those of the Al-Cu matrix alloy under the same test condition, which increased with the increase in temperature and load and with the decrease in TiCp content.

PROPERTIES OF MULTICOMPONENT HIGH-ENTROPY ALLOY AlCrFeCoNi ALLOYED COPPER

The high-entropy alloys AlCrFeCoNiCuх that were prepared by using a vacuum arc meltingmethod are researched. The effects of Al addition on mechanical properties, phase compositionand microstructure were investigated. These AlCrFeCoNiCuх high-entropy alloys exhibit excellentroom-temperature mechanical properties. For AlCrFeCoNiCu0,5 alloy, the microhardnessand elastic modulus reach as high as 6.1 GPa and 109.0 GPa, respectively.

Microstructure and mechanical properties of CoCrFeNiTiAl x high-entropy alloys

CoCrFeNiTiAl x ( x values in molar ratio, x = 0, 0.5, 1.0, 1.5 and 2.0) high-entropy alloys were prepared using a vacuum arc melting method. The effects of Al addition on microstructure and mechanical properties were investigated. The results show that only a face-centered cubic (FCC) crystal structure phase is observed in the CoCrFeNiTi alloy. The phase composition transforms to stabilized body-centered cubic (BCC) structure phases and typically cast dendrite structure appears when Al is added. The dendrite region is rich in Co, Ni, Ti and Al elements while the interdendrite region is rich in Fe and Cr elements. Subgrains and nanosized precipitates are observed in the as-cast CoCrFeNiTiAl alloy. These CoCrFeNiTiAl x high-entropy alloys exhibit excellent room-temperature mechanical properties. For CoCrFeNiTiAl 1.0 alloy, the compressive strength and elastic modulus reach as high as 2.28 GPa and 147.6 GPa, respectively. High density of dimple-like structure is observed from the fracture surfaces of the Al 0 alloy, while alloys with Al addition show typical cleavage fractures with river-like patterns and cleavage steps.

Solid solution alloys of AlCoCrFeNiTix with excellent room-temperature mechanical properties

Alloys with composition of AlCoCrFeNiTix (x: molar ratio; x=0,0.5,1,1.5) were designed by using the strategy of equiatomic ratio and high entropy of mixing. The alloy system is composed mainly of body centered cubic solid solution and possesses excellent room-temperature compressive mechanical properties. Particularly for AlCoCrFeNiTi0.5 alloy, the yield stress, fracture strength, and plastic strain are as high as 2.26GPa, 3.14GPa, and 23.3%, respectively, which are superior to most of the high-strength alloys such as bulk metallic glasses.

Nucleation and Growth of Environment-Induced Monoclinic Phase in Yttria–TZP Ceramics

By careful control of grain size and by the addition of small amounts of stabilizing oxide, usually yttria, zirconia ceramics may be produced with a tetragonal structure that is metastable at both room and intermediate temperatures. These ceramics are termed tetragonal zirconia polycrystalline (TZPs) and can have excellent room-temperature mechanical properties, e.g., strength in excess of 1000 MPa and a toughness approaching 10 MPa m. These outstanding properties are the consequence of the wellestablished transformation toughening mechanism associated with a stress-induced shear transformation from the metastable tetragonal to the equilibrium monoclinic phase at the crack tip. The good mechanical properties of TZPs have led to their use in applications ranging from large cutting blades for processing equipment to femoral heads in hip prostheses. Unfortunately, the transformation from the tetragonal to the monoclinic may also be induced by the environment. This environment-induced transformation proceeds from the surface into the bulk of the material as a function of time. The monoclinic layer so produced is heavily cracked and does not exhibit any transformation toughening, and, consequently, mechanical performance is degraded. In acid solutions, the transformation in TZPs and zirconiatoughened aluminas (ZTAs) occurs rapidly at, and slightly above, room temperature [1±3], but in water, temperatures in excess of 80 8C are required for a readily measurable transformation rate [3±8]. There is much information on the environment-induced transformation at, what may be termed, the macroscopic level, e.g., data on the timeand temperaturedependence of the thickness of the monoclinic layer and the associated degradation in mechanical properties, but there is a dearth of data at the microstructural level. While early work [9] demonstrated the possibility of the transformation taking place slowly in simulated body solution at 37 8C, more recent studies on the small-grain-size, high-purity TZPs currently used for femoral heads have produced no evidence for the transformation in vivo at 37 8C or in vitro [10, 11]. Nevertheless, for the future development of TZPs for prosthetic applications, it is necessary to carry out studies to improve knowledge of the transformation at the microscopic level. This letter reports the results of such a study. Standard femoral heads that had been produced from powder containing 3 mol % yttria by cold isostatically pressing, pressureless sintering and hot-pressing to give a high density of 6.1 Mg my3 were supplied by Norton Desmarquest Fine Ceramics (France). The heads had been polished to a ®ne ®nish of Ra , 3 nm. Twenty heads were aged for up to 30 h in an autoclave operating at 134 8C and 2 bars; for future ease of reference, the polar and equatorial positions are de®ned in Fig. 1. The volume fraction of the monoclinic phase, Xm, produced by the aging treatment was determined from X-ray diffraction (XRD) data using [12]:

A novel multi-layer spray deposition

A novel spray deposition technology with the characteristics of multi-layer deposition, the combination of forced external cooling and internal water-cooling of the substrate was developed. Compared with the conventional spray deposition technology, the novel technology exhibits the specific advantages, including larger solidification rate, higher dimensional precision, and ease to manufacture large preforms. The law of multi-layer spray deposition was studied, and Al-Fe-V-Si alloy with good high-temperature mechanical properties and 6066Al/SiCp composites with excellent room-temperature mechanical properties are prepared by this novel technology.

Tetragonal zirconia polycrystal (TZP)—A review

Tetragonal zirconia polycrystal (TZP) is a new type of zirconia-based engineering ceramic. TZP ceramics are attractive because of their excellent room-temperature mechanical properties, which include flexural strength values over 1 GPa and a fracture toughness greater than 15 MPam 1 2 . These, combined with superior wear properties and a thermal expansion coefficient close to that of iron and iron-based alloys, give rise to a class of desirable engineering ceramics. This review will attempt to summarise the considerable amount of work done on the microstructural development and mechanical properties of TZP, especially over the last few years. The paper is divided into four main sections: 1. (a) The ZrO 2Y 2O 3 phase diagram. 2. (b) Development and optimisation of Y-TZP. 3. (c) Low-temperature ageing of TZP. 4. (d) TZP developed by means of the ZrO 2CeO 2 system