Volume 110, Issue 7

It is important to establish the quantitative effect of graphite's 3D morphology on the thermal conductivity of vermicular graphite iron. In the present study, X-ray tomography is utilized to investigate the 3D morphology of graphite in vermicular graphite iron with different vermicularity. A 3D finite element model was built on the basis of graphite's 3D morphology and the equivalent thermal conductivity of vermicular graphite iron can be calculated. The results show that the volume of graphite clusters in vermicular graphite iron is distributed according to y = a (1 − e − bx ) c exponential function. The higher the vermicularity, the more obvious the polarization of graphite volume. Compared with vermicularity, 3D connectivity of graphite is a more appropriate characteristic parameter to investigate the thermal conductivity of vermicular graphite iron from the 3D morphology point of view.

The liquidus of the ternary system ZnO–“FeO 1.5 ”–SiO 2 in air has been experimentally investigated in the tridymite and cristobalite, spinel, and zincite primary phase fields in the temperature range 1623–1923 K (1350–1650°C). Slags containing up to 65 mol.% “FeO 1.5 ” have been studied for the first time. The slag–spinel–zincite eutectic in the binary ZnO–“FeO 1.5 ” system in air has been estimated by extrapolation of the low-SiO 2 part of the ternary system to x (SiO 2 ) = 0. High-temperature equilibration on primary phase (silica) or inert metal (platinum) substrates, followed by quenching and direct measurement of Zn, Fe and Si concentrations in the equilibrium phases with electron probe X-ray microanalysis has been used to accurately characterize the system in equilibrium with air. The discrepancies of the previous experimental work in this system have been resolved. The obtained data have been used to reoptimise the existing thermodynamic model.

The influence of high pressure torsion (HPT) on the formation and decomposition of solid solutions in the copper–silver system has been studied. The investigated Cu-8 wt.% Ag alloy was annealed at two different temperatures, 500 and 650°C, and quenched. The samples consisted of (Cu) solid solution in the matrix with (Ag) precipitates. During HPT a steady-state value of torsion torque was reached after about 1.5 anvil rotations. After HPT (5 anvil rotations) the composition of the (Cu) solid solution in both samples had become equal. In other words, the concentration of silver in the (Cu) matrix annealed at 650°C decreased and in the sample annealed at 500°C increased. Moreover, a similar process took place in (Ag) precipitates as well. The concentration of copper in (Ag) particles in the sample annealed at 650°C decreased and in the sample annealed at 500°C increased. Thus, the composition of (Cu) and (Ag) solid solutions reached at steady-state during HPT does not depend on that before HPT. The composition of the (Cu) and (Ag) solid solutions after HPT is as high as if the samples were annealed at a certain intermediate temperature about 600 ± 20°C.

The effect of cerium on the high-temperature oxidation behavior of low sulfur martensitic stainless steel 1Cr13Mo was investigated at 700°C, 800°C and 900°C in air, and then analyzed by means of X-ray diffraction, energy dispersive X-ray spectroscopy and electron probe microanalysis. The external scales formed on samples are composed of Cr 2 O 3 and MnCr 2 O 4 at 700°C and 800°C. When at 900°C, only M 2 O 3 type oxide can be found in the scale of the sample without cerium, and there is still some MnCr 2 O 4 that can be detected in the scale of the sample containing cerium, showing cerium benefits forming MnCr 2 O 4 which makes the scale more protective. After oxidation at 900°C, in the sample containing cerium, segregation of cerium and chromium is found near the metal/scale interface, which indicates that cerium reduces the oxidation rate by modifying the transport process, changing the transportation mechanism from Cr 3+ ions' outward diffusion into O 2− anions' inward diffusion. Meanwhile, the sample containing cerium shows a smaller number of pores and lower sulfur content near the interface compared with the sample without cerium, which suggests that cerium reduces the pore formation and enhances the scale adhesion.

In this paper, the effects of copper addition (0–2.0 wt.%) on the microstructure and properties of carbidic austempered ductile iron were studied using an optical microscope, a scanning electron microscope, a Rockwell hardness tester, a pendulum impact tester, an X-ray diffractometer, a block-on-ring wear testing machine and an electrochemical tester. The amount of carbides and graphite nodules simultaneously decreased with the increase in Cu content. Cu also improved the nodularity of graphite, made the graphite nodules grow, increased the pearlite content and refined the pearlite. After austenitizing (900°C / 100 min) and austempering (300°C / 100 min), the amount and size of the acicular ferrite significantly reduced with the addition of Cu. In contrast, the amount of retained austenite dramatically increased, and the carbon content in retained austenite slightly increased. The hardness of carbidic austempered ductile iron had no obvious change with the increase in Cu content. The wear resistance of carbidic austempered ductile iron first increased and subsequently decreased, and the impact toughness and corrosion resistance were improved with the increase in Cu content. The comprehensive properties of carbidic austempered ductile iron were optimal, with the Cu content of 1.0 wt.%.

In this work, fabrication and characterization of aluminum gradient composites reinforced by nano-particles of tungsten carbide via the centrifugal casting method were studied. In order to prepare a mixture of aluminum and tungsten carbide powders, a high energy planetary ball mill was used. The master-alloy was added to A356 aluminum matrix by horizontal centrifugal casting at different rotation speeds to synthesize Al-5 wt.% WC. The results of X-ray diffraction and scanning electron microscopy analysis confirmed a homogeneous powder in nanometer scale through mechanical milling. Centrifugal casting at speeds of up to 1300 RPM is a suitable method for production of Al–WC gradient nano-composites. By increasing the rotation speed, reinforcement phases are transmitted into the outer layers of cast samples. An agglomeration of hard WC phase leads to improvement of surface hardness and wear resistance.

In this work, Ti 43.3 Zr 21.7 Ni 7.5 Be 27.5 (at.%) bulk metallic glass and Zr 76.11 Ti 4.20 Cu 4.51 Ni 3.16 Be 1.49 Nb 10.53 (at.%) bulk metallic glass composite are used to butt-weld identical alloy specimens using a fiber laser beam under a vacuum. Thereafter, various tests are conducted on the welded specimens to evaluate the applicability of the laser welding process to bulk metallic glasses and bulk metallic glass composites. Crystallization is suppressed during the welding process as much as possible, and welded Ti-based bulk metallic glass and Zr-based bulk metallic glass composite exhibit their original properties although some crystalline phases are formed in the welding fusion zone in Ti-based bulk metallic glass. Therefore, laser welding under a vacuum is appraised as a feasible technology to join bulk metallic glasses and bulk metallic glass composites.

In this work, the quadratic regression orthogonal rotation design has been applied to optimize the composition and mechanical properties of a novel biomedical Zr-based alloy system. Combined with the statistical package for the social sciences (SPSS) analysis, a mathematical model is proposed to assess the influence of Cu, Nb and Sn contents on the elastic modulus of the alloy system. The optimal alloy composition can be determined based on the regression modeling. The experimental results exhibit the role of Nb content on mechanical properties of the Zr alloys. It is indicated that the as-cast Zr-4 at.% Cu-1.5 at.% Sn- x at.% Nb ( x = 0, 7.5 and 15) alloys are mainly composed of α-Zr and Zr 3 Cu phases. Nb addition results in the formation of β-Zr and fine uniformly-distributed secondary phase Zr 3 Cu. The Zr-based alloy system exhibits low elastic modulus (19.55–32.46 GPa), moderate compression strength (1904–1117 MPa), yield strength (543–1078 MPa) and high elastic energy (7.19–18 MJ m –3 ). The Zr-4 at.% Cu-1.5 at.% Sn-7.5 at.% Nb alloy shows an elastic modulus of 19.55 GPa, which is comparable to that of human bones. These optimized Zr-4 at.% Cu-1.5 at.% Sn- x at.% Nb alloys can be considered as potential candidates for biological hard-tissue substitute materials.

Mo 2 FeB 2 -based cermets were prepared with various Mo/B atomic ratios in the range of 0.8 to 1.1. The microstructure and crystalline phases were studied through scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, energy dispersive X-ray analysis and X-ray diffractometry. The results indicated that as the Mo/B atomic ratio increased, the morphology of the hard phase gradually transformed from long-strip to near-equiaxed. The tendency of transformation in the range of 1.0 to 1.1 was more significant. Two typical cermet samples (Mo/B = 1.0, Mo/B = 1.08) of different morphologies were studied with transmission electron microscopy. As the Mo/B atomic ratio increased, the average particle size decreased, inhibiting the nucleation of the particles, the anisotropy of different crystallographic planes reduced, the particles transformed from long-strip to the near-equiaxed shape. Moreover, it could be found from X-ray diffractometry results that the disparity between the crystal lattice constants c and a gradually diminished and the surface tension differences of the amorphous surfaces decreased, resulting in the anisotropy of different crystal-lographic planes gradually decreasing. The cermets with Mo/B = 1.02 demonstrated the highest transverse rupture strength, as well as the hardness and improved fracture toughness values of 2367.5 ± 50 MPa, 88.2 ± 0.1 HRA, and 27.6 ± 0.5 MPa · m 1/2 , respectively.

This study is focused on mechanical and tribological performance with phase and crystal structure studies of diffusion bonded dense α-alumina laminates with chemically activated Al–Sr mixed hydride (SrH 2 /Sr 2 AlH 7 ) nano-particles as the interlayer by developing a controlled interlayer for preparing oxide laminate composites with high fracture toughness and enhanced wear resistance. Shear bond strength and four-point bending tests indicated a maximum strength of 174 and 189 MPa for hot pressed alumina/Sr 2 AlH 7 , with a transgranular fracture mechanism under shear stress. The difference in the coefficient of thermal expansion between the composites layers resulted in the development of residual stresses in alumina and interlayer. The magnitude and the distribution of these micro and macro residual stresses were assessed by the piezo-spectroscopic technique. The effects of residual stress on fracture toughness and the friction coefficient of laminates were studied.

A flower-like SnO/ZnO heterojunction photocatalyst with high catalytic activity was synthesized by a simple ultrasonic reaction method. Results show that the SnO/ZnO composites consist of SnO, SnO 2 , and ZnO. The flower-like structure is made of many SnO nanosheets with a thickness of approximately 20 nm and length of 1–2 μm. A tight interface combination of SnO, SnO 2 , and ZnO clearly improves the photoactivity of SnO. The photocatalytic performance of the SnO/ZnO composite is much higher than that of ZnO raw materials and SnO sample. The degradation rate of the methyl orange of the SnO/ZnO composite is 99% within 60 min under visible-light irradiation.