Effects of interfacial strength on fatigue crack growth in a fiberreinforced Ti-alloy composite

The fatigue crack growth behavior of a Ti-6A1-4V composite with boron fibers was previously studied in the as-received and thermally exposed conditions. Fracture strengths of the composite, fiber, and interface were characterized together with fatigue crack growth rates and failure mechanisms. Utilizing the matrix and fiber properties as input, a recently proposed model was exercised to elucidate the effects of interfacial strength on crack growth rates in the composite. Comparison of experimental results with model calculations revealed that a weak fiber/matrix interface combined with a strong, high-modulus fiber led to interface debonding and crack deflection and produced the beneficial effects of increased threshold and reduced transverse crack growth rates. This paper is based on a presentation made in the symposium “Interfaces and Surfaces of Titanium Materials” presented at the 1988 TMS/AIME fall meeting in Chicago, IL, September 25–29, 1988, under the auspices of the TMS Titanium Committee.     

Phase composition and structure of composite powders based on solid solutions of SiC and AlN

The structure of SiC–AlN powders is investigated by x-ray diffraction and transmission electron microscopy methods. The powders were produced by joint carbon reduction and nitriding of silicon and aluminum oxide mixtures. The results show that a mixture of solid solutions forms during joint SiC and AlN synthesis at 1700°C, with SiC forming β (3C) and α (2H) modifications with different grain morphology. The fiber form is characteristic of β-SiC, whereas the grains of the solid solution based on SiC have a predominantly equiaxed form. α-SiC grain dimensions are considerablys smaller than those of AlN. Institute of Materials Science, National Academy of Sciences of Ukraine. Kiev Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 81–86, July–August, 1997.     

Corrosion of an Aluminum Matrix Composite in situ Based on Al–7Si–1Fe Alloy

The results of a comparative research into the corrosion resistance of an aluminum matrix composite material produced by the oxygen lancing of a prehydrogenated aluminum alloy melt based on Al–Si–Fe with an iron content of over 1.0% and Al–7% Si alloy with an iron content of up to 0.3% modified by ligature 5Al–Ti for 2% are shown. The aluminum-alloy corrosion was conditioned by the film discontinuity of the oxide on some phases, primarily Al5SiFe. The composite and reference alloy-sample couples with a diameter of 15 mm and a length of 50 mm were put to the test in a 7% solution of NaCl salt fog in SFC-1 chamber on suspension brackets at a temperature of 22°C for 300 h. The results show the mass loss close values of the samples, despite the significantly higher iron content in the composite, because particles 100–200 nm in size formed in the melt by lancing are deposited on the composite phase boundaries, reducing the interaction surface area with the corrosive environment. The researched composite material can be recommended as a corrosion-resistant alternative to alloys with elevated iron content, which are used for high pressure die casting (HPDC).     

Thermal conductivity and thermal expansion of graphite fiber-reinforced copper matrix composites

The high specific conductivity of graphite fiber/copper matrix (Gr/Cu) composites offers great potential for high heat flux structures operating at elevated temperatures. To determine the feasibility of applying Gr/Cu composites to high heat flux structures, composite plates were fabricated using unidirectional and cross-plied pitch-based P-100 graphite fibers in a pure copper matrix. Thermal conductivity of the composites was measured from room temperature to 1073 K, and thermal expansion was measured from room temperature to 1050 K. The longitudinal thermal conductivity, parallel to the fiber direction, was comparable to pure copper. The transverse thermal conductivity, normal to the fiber direction, was less than that of pure copper and decreased with increasing fiber content. The longitudinal thermal expansion decreased with increasing fiber content. The transverse thermal expansion was greater than pure copper and nearly independent of fiber content. formerly with NASA Lewis Research Center, is retired David L. McDanels, This article is based on a presentation made in the symposium “High Performance Copper-Base Materials” as part of the 1991 TMS Annual Meeting, February 17–21, 1991, New Orleans, LA, under the auspices of the TMS Structural Materials Committee.     

Damage mechanisms and fiber orientation effects on the load-bearing capabilities of a NEXTEL/BLACKGLAS low-cost ceramic composite

In this article, the fiber orientation effect on the load-bearing capabilities of a NEXTEL/BLACKGLAS low-cost composite was experimentally investigated, and damage mechanisms were analyzed. Ultrasonic nondestructive evaluation (NDE) was performed to interrogate the composite samples before testing. A four-point bending test was conducted to study the mechanical behavior. Scanning electron microscopy (SEM) fractography and SEM energy-dispersive X-ray spectroscopy (EDXS) along with SEM/EDXS elemental mapping were employed to characterize damage mechanisms, microstructures, and the microchemical distribution of elements following mechanical tests. A mechanistic understanding of the fracture behavior of the NEXTEL/BLACKGLAS ceramic composite was provided. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee.     

Damage mechanisms and fiber orientation effects on the load-bearing capabilities of a NEXTEL/BLACKGLAS low-cost ceramic composite

In this article, the fiber orientation effect on the load-bearing capabilities of a NEXTEL/BLACKGLAS low-cost composite was experimentally investigated, and damage mechanisms were analyzed. Ultrasonic nondestructive evaluation (NDE) was performed to interrogate the composite samples before testing. A four-point bending test was conducted to study the mechanical behavior. Scanning electron microscopy (SEM) fractography and SEM energy-dispersive X-ray spectroscopy (EDXS) along with SEM/EDXS elemental mapping were employed to characterize damage mechanisms, microstructures, and the microchemical distribution of elements following mechanical tests. A mechanistic understanding of the fracture behavior of the NEXTEL/BLACKGLAS ceramic composite was provided. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee.     

Developing and mastering a technology for making steel with a sulfur content no greater than 15 ppm

The converter shop at the Azovstal’ combine has developed and successfully introduced a technology for making steel that contains no more than 15 ppm sulfur. The combine has already produced commercial batches of tube steel with a maximum sulfur content of 6–15 ppm. Reducing carbon content from 0.10–0.12 to 0.07–0.08% and lowering sulfur content from 40–70 ppm to 6–15 ppm have improved the quality of the metal of the slabs and rolled products made by the combine. Among these improvements: a decrease in axial porosity and axial segregation in the slabs, an improvement in the ductility characteristics of the rolled metal, a reduction in the degree of contamination of plate metal by nonmetallic inclusions, and a decrease in the incidence of plate rejection in ultrasonic tests. __________ Translated from Metallurg, No. 3, pp. 46–49, March, 2006.     

Influence of Aluminum Additives on the Content and Parameters of the Fine Structure of Titanium Silicon Carbide in SHS Powders

The dependence of the phase composition and parameters of a fine structure of titanium silicon carbide in powders formed by the self-propagating high-temperature synthesis on the aluminum concentration in the 5Ti/2Si/1C reaction mixture is investigated. The aluminum content is varied in a range of 0.1–0.4 mole fraction with the conservation of the total carbon content. It is established that the additives of aluminum not only affect the yield of titanium silicon carbide, but also promote the preferential formation of Ti5Si3 in synthesis products instead of TiSi2 identified in powders containing no aluminum. The introduction of a small amount of aluminum (0.1 mole fraction) leads to the formation of the Ti3Si1 – xAlxC2 solid solution and makes it possible to decrease the content of impurity phases in SHS powders by 6%. The silicon carbide concentration in SHS powders decrease at a higher aluminum content in the reaction mixture, while that of binary compounds (TiC, Ti5Si3, TiAl) correspondingly increases. No noticeable effect from the introduction of aluminum on the parameters of the crystal lattice of titanium silicon carbide in SHS powders is found in concentration limits of 0.1–0.25 mol %. A noticeable increase in parameters of a and c for Ti3Si1 – xAlxC2 (from a = 3.067 Å, c = 17.67 Å to a = 3.07 Å, c = 17.73 Å) with the conservation of the c/a ratio in limits of known values (c/a = 5.78) is observed only with the aluminum concentration of 0.4 mole fraction. The crystallite size of titanium silicon carbide depends, first and foremost, on the combustion parameters. At the same time, the deformation of the crystal lattice of Ti3Si1 – xAlxC2 in SHS powders increases monotonically with an increase in the aluminum content in the reaction mixture in the concentration range under study.     

Synthesis and physicomechanical properties of B4C-VB2 composites

We have studied the properties of composites in the B₄C-VB₂-C system, obtained by reaction synthesis with hot pressing. We have established that the presence of free carbon and vanadium boride in the ceramic makes it possible to activate the sintering process and to obtain a dense, highly dispersed ceramic with good structural homogeneity parameters for lower isothermal holding temperatures. The composite ceramic has higher hardness and bending strength over a broad range of vanadium boride content than the monophase ceramic based on boron carbide. The strength properties of the composite ceramic containing up to 8 vol.% vanadium boride are improved by means of a mechanism involving propagating cracks bending around obstacles. When the VB₂ concentration increases further, the properties of the composite are determined by a microcracking mechanism. In this case, we observe relatively small changes in the elastic characteristics, which depend linearly on the composition of the ceramic. Introducing vanadium boride into the material is also accompanied by an increase in the contact and microstructural strengths. The results obtained indicate that the new composite material is promising for fabricating wear-resistant and shock-resistant components of various structures and machines. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 59–72, January–February, 2006.     

Fiber-Matrix interactions in brittle matrix composites

Brittle matrix composites, including carbon-carbon (C-C) and ceramic matrix, offer a new dimension in the area of high-temperature structural materials. Fiber-matrix interactions determine the mechanism of the load transfer between the fiber and matrix and resulting mechanical properties. Composites studied in this work include a C-C composite densified with a chemical vapor infiltration (CVI) pyrolytic carbon, silicon carbide fiber-silicon carbide matrix composite, and carbon fiber-silicon carbide matrix composites densified by the CVI technique. The type of the interfacial carbon in C-C composites was found to control their mechanical properties. The presence of the compressive stress exerted by the matrix on the carbon fibers was attributed to an increase in flexural strength. The transverse matrix cracking in C/SiC composites was believed to cause a lowering in the flexural strength value. Brittle fracture behavior of SiC/SiC composites was correlated with the presence of an amorphous silica layer at the fiber-matrix interface. This invited paper is based on a presentation made in the symposium “Structure and Properties of Fine and Ultrafine Particles, Surfaces and Interfaces” presented as part of the 1989 Fall Meeting of TMS, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Structures Committee of ASM/MSD.     

Structure and high-temperature strength of composite materials based on boron nitride

The structure and physicomechanical properties of composite materials based on boron nitride within which new phases (mullite and sialon) form during hot compaction are studied. It is established that the microstructure of composites is specified by their texture formation caused by the crystal morphology of boron nitride particles and it is almost independent of composite phase composition. It is shown that the main factor that affects strength is porosity. The dependence of strength on porosity is exponential in character. The strength of boron nitride-mullite and boron nitride-sialon composites is 110–140 MPa and at 20–1200°C it is almost unchanged. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 33–39, May–June, 2006.     

Theory, manufacturing technology, and properties of powders and fibers

The properties of ferromagnetic powders after reduction annealing are examined. It is shown that magnetite and a destructured composite organic coating ensure the resistance of such powders to external effects. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 7–8 (456), pp. 3–7, 2007.     

Composite Micropelletization of Slime for Iron Grade and Recovery Maximization to Generate Pellet Feed Materials

The present research work deals with the upgradation of iron ore slime by maximizing its iron grade and recovery so that it can be used in downstream iron making processes. Slime contains significant amount of iron value and is still being dumped as waste which also requires large area for dumping. Slime (45–48 wt% Fetotal) after converting into dry powder was mixed with desired amount of reductant (NCC), and the mixture was converted into composite micropellets (+ 1 to − 6 mm) by using disc pelletizer. Produced composite micropellets were subjected to reduction at desired reduction conditions. Temperature, NCC dosage and time were the prime parameters whose effect on iron grade and recovery was investigated. Wet magnetic separation tests were performed on reduced samples to upgrade the iron content. Maximum value of iron grade and recovery was achieved at 900 °C with 11% of NCC for 60 min. After magnetic separation, iron content and recovery in the magnetic concentrate were 57.27% and 60%, respectively. This route of reduction for steel plant generated slime may be a helping hand in the usage of slime to prepare magnetic concentrate-based pellet feed materials.     

Influence of cold rolling and annealing on the microstructure,mechanical properties,and electrical conductivity of an artificial microcomposite Cu-18% Nb alloy

The influence of cold rolling and subsequent annealing at different temperatures on the micro-structure, strength properties, and electrical conductivity of a microcomposite Cu-18% Nb alloy fabricated by bundling and deformation is studied. A composite billet is rolled up to a total true strain of 3.5 and 5.1. After rolling, a nanocrystalline structure is obtained with an average filament width of 70–100 nm depending on the rolling strain. The ultimate tensile strength of the rolled foils is 867–934 MPa and the electrical conductivity is 19–40% of the pure copper conductivity. It is shown that annealing at 550°C results in an increase in the conductivity from 40 to 60% at a retained strength (microhardness) of the alloy.     

Reaction zone microstructure in a Ti3Al + Nb/SiC composite

A composite of Ti-25Al-13Nb (atomic percent) matrix with a continuous SiC fiber (SCS-6) reinforcement was fabricated by hot pressing powder cloths and mats of fiber. The fiber/matrix reaction zone was studied using scanning electron microscopy (SEM) and transmission electron microscopy/analytical electron microscopy (TEM/AEM) techniques. The extent of reaction was determined, phases were identified, and solute partitioning among the phases was determined. It was found that the matrix had reacted only with a portion of the carbon-rich outer layer of the SCS-6 fiber. The reaction zone contained two concentric zones which are distinguished by the presence of different carbide phases. Both zones contained a hexagonal Si-bearing phase, and one of the zones also contained some fine scattered porosity. The results are discussed with reference to available phase equilibria data. This paper is based on a presentation made in the symposium “Interfaces and Surfaces of Titanium Materials” presented at the 1988 TMS/AIME fall meeting in Chicago, IL, September 25–29, 1988, under the auspices of the TMS Titanium Committee.     

Development and creation of layered materials for tool purposes with a prescribed property gradient

Layered composite materials based on hard alloys grades VK and TK with graded surface properties are studied. The materials are prepared using standard procedures of thermal diffusion impregnation, deposition from the vapor phase, and ion-plasma deposition. In addition dispersion strengthened hard alloys are prepared by processing in Ti plasma between the stages of preliminary and final sintering. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 30–38, July–August, 2006.     

Effect of a strengthening phase on the structure and some mechanical properties of electrolytic coatings based on nickel

An investigation was made of the composition, structure, microhardness, and tribological properties after thermochemical treatment of composite electrolytic nickel-based coatings with various additions. It was established that the mear resistance of nickel-boron-diamond coatings in sliding friction without lubrication depends upon the nature and amount of added inclusions, and the mechod of treatment. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 47–51, May–June, 1998     

Composition and structure of silicon oxycarbide fibers

The composition and structure of Si_xC_yO_z glassy fibers that form during carbonization of hydrated cellulose impregnated with silicon dioxide is studied by Auger-electron spectroscopy, chemical analysis, transmission and scanning electron microscopy. It is established that the surface layer of a fiber to a depth of 30 nm consists of oxycarbide phase SiC_1.1O_1.8 with chemically absorbed oxygen and nitrogen, but the inner layers are two-phase that apart from this phase contain amorphous carbon. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 7–9, July–August, 2006.     

Effect of fiber volume fraction on the fracture behavior of Nb-1 Wt pct Zr/218W composites at elevated temperatures

Nb-1 wt pct Zr/218W long-fiber composite monotapes, nominally containing 0 to 70 vol pct of 218 tungsten fibers, were fabricated by arc spraying the Nb-1 pct Zr matrix onto the tungsten fibers. The monotapes were consolidated by hot pressing and hot isostatic pressing techniques. Tensile tests conducted between 1400 and 1600 K, under engineering strain rates varying between 1.5×10⁻⁵ and 1.5×10⁻³ s⁻¹, demonstrated that composites containing 70 vol pct of fibers had the highest strength-to-density ratio. Microstructural observations of specimens tested at 1400 K revealed that composites containing less than 50 vol pct of fibers showed extensive matrix cavitation, fiber-matrix debonding, and necking of the fibers. Above 50 vol pct, the composite matrix was less prone to cavitation, with an increasing tendency toward shear deformation of the fibers as the fiber volume fraction increased. No fiber damage was observed at 1400 K away from the fractured end, but significant fiber damage was observed at higher temperatures. A phenomenological model is presented to rationalize these observations. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee.