T. Sakata

Microstructural characterization of TiB in in situ synthesized titanium matrix composites prepared by common casting technique

Abstract TiC reinforced titanium matrix composites were produced by non-consumable arc-melting technology utilizing the self-propagation high-temperature synthesis (SHS) reaction between titanium and graphite. X-Ray diffraction (XRD) was used to identify the phases in the composites. Microstructures of the composites were observed by optical microscope (OM) and transmission electron microscope (TEM). The results show that there are two phases in the composites: TiC and titanium matrix alloy. TiC has two different shapes: dendritic shape, equiaxed or near-equiaxed shape. The in situ synthesized TiC grows by dissolution–precipitation. Analysis of the binary phase diagram determined that the solidification path undertook the following three stages: primary TiC, binary eutectic β-Ti+TiC and solid transformation. Primary TiC grows in dendritic shape due to the formation of composition undercooling. Binary eutectic TiC grows in equiaxed or near-equiaxed shape. A small quantity of TiC may form twin structure during nucleation and growth. The twin plane is the (111) plane.

Microstructure and tensile properties of in situ (TiB+TiC)/Ti6242 (TiB:TiC=1:1) composites prepared by common casting technique

In the present work, (TiBw+TiCp)/Ti6242 composites with TiB:TiC=1:1 were produced by common casting and hot-forging technology utilizing the SHS reactions between titanium and B4C, C powder. The microstructures of composites were examined using optical microscopy (OM) and transmission electron microscopy (TEM). The X-ray diffraction (XRD) was used to identify the phases that were present in the composites. There are three phases — TiB, TiC and titanium matrix alloy. TiB grows in short-fiber shape, whereas TiC grows in dendritic, equiaxed or near-equiaxed shape. TiB whiskers were made to align the longitudinal direction and TiC dendritic was broken up after hot-forging. The reinforcements are distributed uniformly in matrix alloy. The interfaces between reinforcements and titanium matrix alloy are very clean. The tensile strength (yield strength and ultimate tensile strength) and the Youngs modulus improve with the addition of TiB whiskers and TiC particles although some reduction in ductility is observed. (TiBw+TiCp)/Ti6242 composites with TiB:TiC=4:1 will fracture on a lower level of applied stain due to deformation restraint of TiB whiskers on titanium matrix alloy. The (TiBw+TiCp)/Ti6242 composites with TiB:TiC=1:1 show higher tensile strength and ductility. The addition of graphite not only improves the tensile strength and the Youngs modulus but also increases the ductility. The improved Youngs moduli and increased tensile strengths of the composites are explained using shear lag and rule-of mixtures theories. The Youngs moduli of the composites were found in good agreement with that calculated from Tsai–Halpin equation applied for discontinuous-reinforced composites.

Microstructure and tensile properties of in situ synthesized (TiBw + TiCp)/Ti6242 composites

In the present work, (TiBw+ TiCp)/Ti6242 composites were fabricated via common casting and hot-forging technology utilizing the SHS reaction between titanium and B4C. The XRD technique was used to identify the phases of composites. The microstructures were characterized by means of OM and TEM. Results from DSC and analysis of phase diagram determine solidification paths of in situsynthesized Ti6242 composites as following stages: β-Ti primary phase, monovariant binary eutectic β-Ti + TiB, invariant ternary eutectic β-Ti + TiB + TiC and phase transformation from β-Ti to α-Ti. In situsynthesized reinforcements are distributed uniformly in titanium matrix alloy. Reinforcement TiB grows in whisker shape whereas TiC grows in globular or near-globular shape. TiB whiskers were made to align the hot-forging direction after hot-forging. The interfaces between reinforcements and Ti matrix alloy are very clean. There is no any interfacial reaction. Moreover, the mechanical properties improved with the addition of TiB whiskers and TiC particles although some reduction in ductility was observed. Fractographic analysis indicated that the composites failed in tension due to reinforcements cracking. The improvements in the composite properties were rationalized using simple micromechanics principles. The strengthening mechanisms are attributed to the following factors: undertaking load of TiB whiskers and TiC particles, high-density dislocations and refinement of titanium matrix alloys grain size.

Microstructures and La-rich compounds in a Cu-containing hypereutectic Al-Si alloy

Abstract In the present study, microstructural variations and compounds with the addition of 3 wt.% La into casting A390 alloy were investigated through optical microscopy, transmission electron microscopy, scanning electron microscopy. Energy dispersive X-ray mapping and point analysis are conducted for phase identification purposes. The results show that the addition of 3 wt.% La has little modification effect on silicon phases in A390 as expected for the formation of the compounds Al7Si7Cu2La3.5 and Al5Mg8Cu6Si6.

Preparation and characterization of cerium oxide ultrafine particles dispersed in polymer thin films

Abstract Cerium(IV) oxide ultrafine particles were prepared using the thermal relaxation technique known as the relaxative auto-dispersion (RAD) process. The ultrafine particles obtained were characterized by high-resolution electron microscope (HREM) observations and ultraviolet-visible spectra measurements. HREM micrographs revealed that cerium oxide ultrafine particles were uniformly dispersed and individually isolated in the matrix. The size distribution of the nm-sized cerium oxide particles was fairly narrow. Selected-area electron diffraction patterns of the particles were completely indexed as those of cerium(IV) oxide with cubic fluorite structure, and the lattice constant calculated from the radii of the Debye-Sherrer rings was 5.41 A. Absorption spectra of the ultrafine particles in the composite film were compared with those of the bulk material. However. there were no size quantization effects on the absorption edge of CeO2.

Tensile properties of in situ synthesized titanium matrix composites reinforced by TiB and Nd2O3 at elevated temperature

Abstract Titanium matrix composites reinforced with TiB and Nd 2 O 3 were prepared by a non-consumable arc-melting technology. X-ray diffraction (XRD) was used to identify the phases in the composites. Microstructures of the composites were observed by means of optical microscope (OM). There are three phases: TiB, Nd 2 O 3 and titanium matrix. TiB grows in needle shape, whereas Nd 2 O 3 grows in lath shape. Tensile properties of the composites were tested at 773, 823 and 873 K. Both the fracture surfaces and longitudinal sections of the fractured tensile specimens were comprehensively examined by scanning electron microscope (SEM). The fracture mode and fracture process at different temperatures were analyzed and explained. It shows that the tensile strength of the composites has a significant improvement at elevated temperatures compared to titanium matrix. The ductility of the composites improves with the content of neodymium and the test temperatures. The titanium composite exhibits different fracture modes at different test temperatures.

Dry sliding friction and wear behavior of woodceramics/Al–Si composites

Abstract Woodceramics/AlSi (WCMs/AlSi hereafter) composites were prepared by means of high-pressure vacuum infiltration of liquid alloy into woodceramics. The friction and wear behavior of WCMs/metal composites at various applied loads and sliding velocities was investigated by using a block-on-ring test at room temperature under dry conditions. Furthermore, the morphologies, phases and element valences of the worn surface and debris were observed, examined and analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray microanalysis (EDAX) and X-ray photoelectron spectroscopy (XPS), respectively. In addition, load and sliding velocity dependence mechanisms of the wear and friction behavior of the composite and matrix alloy were discussed. Experimental results show that WCMs/AlSi composites have a topologically uniform interconnected network microstructure. Their tribological properties are improved dramatically, compared to those of the matrix AlSi alloy, due to the formation of wide, compacted surface carbon films. The wear mechanisms of WCMs/AlSi composites and of the matrix alloy vary with applied load from mild to severe wear.

Microstructure and properties of ecoceramics/metal composites with interpenetrating networks

Abstract Ecoceramics is a porous carbon material which is proved to have some favorable characteristics. With the purpose of enlarging the application fields of ecoceramics, an ecoceramics/ZK60A (ECMs/ZK60A hereafter) composite was fabricated using high-pressure vacuum infiltration technique. Microstructural analysis and measurements of mechanical properties as well as damping behavior of ECMs/ZK60A composite were made. Experimental results show that ZK60A filled most of the pores and ECMs/AlSi composites have a topologically uniform interconnected network microstructure. ECMs/ZK60A composite exhibited superior mechanical properties as compared with uninfiltrated ecoceramics. It is believed that strengthening effect was caused by strengthening of ZK60A, crack bridging by the ductile phase and interlocking structure between components in ECMs/ZK60A composite. Damping values of ECMs/ZK60A composite improve based on those of ecoceramics. They increase with testing temperature but decrease with increasing vibration frequency.

Interfacial structure and mechanical properties of MgLi matrix composites

The study on interfacial structure and tensile properties of MgLi matrix composites. The results showed that there was a clear interface between the MgLi matrix and SiC whiskers. Calculation of thermodynamics confirmed that the clear interface between the matrix and SiC whiskers may contribute to the low reactionary potential or the low reactionary dynamics. However, some SiC whiskers were attacked. As a result, SiC whiskers connected with matrix in {111} and formed 70.5° or 109.5° stages on the whiskers surface in {111} face. The reason was the lower interfacial energy of {111} face. Tensile test confirmed that the SiCw /MgLiAl composites showed higher tensile strength and higher modulus compared with MgLi matrix. Moreover, the specific strength and specific modulus were also increased obviously.

Interfacial microstructure of TiB/Ti in a Ti-TiB-TiC in situ composite

A common casting technique has been applied to fabricate Ti-TiB-TiC in situ composite utilizing the self-propagation high-temperature synthesis (SHS) reaction between Ti and B4C. The microstructure of TiB/Ti interfaces has been investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM). The TiB/Ti interfaces are atomically flat, sharp and free from any interfacial phase. TiB is also well bonded with the matrix. The following consistent crystallographic relationships between TiB and Ti have been observed by HREM, namely, [010]TiB//[0110]Ti, (100)TiB//(2110)Ti, (001)TiB//(0002)Ti, (101)TiB//(4221)Ti and [001]TiB//[0110]Ti, (010)TiB//(2110)Ti, (200)TiB//(0002)Ti. The formation mechanism of TiB/Ti interfaces has been analyzed by solidification theory.