Metallurgical parameters,mechanical properties and machinability of ductile cast iron

Results on the effect of solidification cooling rate on the microstructure, mechanical properties and machinability of spheroidal graphite (SG) iron have been presented. The effect of ferritic heat treatment on the same properties has been also investigated. The microstructural observation, tensile properties and hardness values of the present SG iron has been developed. The tool life criterion was used as a measure of machinability. It was found that during turning of SG iron by using a single point cutting tool, its life increased with decreasing the solidification cooling rate for both sand and metal moulds. The tool life was found to be significantly affected by the variation of nodule characteristics. A decrease in tool life due to an increase of nodule count was observed. The tool life was found to be directly proportional to the ductility of SG iron whether for the as cast or ferritic heat-treated ingots.     

Deposition and microhardness of SiC from the Si2Cl6-C3H8-H2-Ar system

We obtained SiC coating layers on a graphite substrate using hexachlorodisilane (Si₂Cl₆, boiling point 144° C) as a silicon source and propane as a carbon source. We examined the deposition conditions, contents of carbon, silicon and chlorine in the deposits, and the microhardness. Mirror-like amorphous silicon layers were deposited in the reaction temperature range 500 to 630° C. well-formed silicon carbide layers with good adherency to the substrate were obtained above 850° C. The lowest deposition temperature of SiC was estimated to be 750 to 800° C. The Vickers microhardness of the SiC layer was about 3800 kg mm^–2 at room temperature and 2150 kg mm^–2 at 1000° C.     

Fabrication and characterisation of graphite/alumina reinforced copper composites

The infiltration of graphite/alumina preforms with a bronze alloy has been investigated taking into account the influence of the binder type, the graphite/alumina content in the preform and the percentage of binder in water. The preforms showing an acceptable rigidity have been infiltrated with a CuSn12 bronze alloy by squeeze casting considering two different pouring temperatures. The composite produced has been characterised in terms of density, Brinell hardness, coefficient of thermal expansion, as well as friction and wear behaviour. The coefficient of friction for the bronze matrix composite is around 0.17, being three times lower than that shown by the unreinforced copper alloy. Given the contact geometry (ball of steel against a planar sample) and testing conditions (20°C, dry sliding, 40% humidity), the composite wear rate is around twenty times lower that of the bronze, being 10^–6mm²/kg for the composite and 2 × 10^–5 mm²/kg for the bronze.     

Fracture toughness behaviour of ferritic ductile cast iron

The static rate fracture toughness of a series of eight heats of ductile cast iron has been measured. Samples from each heat were tested in a heat treated condition which produced a fully ferritic matrix. The dominant influence of carbide (primarily in e pearlitic form) in controling the fracture toughness was thus eliminated in this study. The chemical composition and the microstructural feature size has also been measured directly from each specimen tested. A multiple linear regression method was used to establish a simple mathematical relationship between fracture toughness and the composition and microstructure. Fracture toughness was found to be strongly associated with the spacing (or size) of the graphite nodules in these fully ferritic ductile cast irons. Other features, including the composition, the ferrite grain size, or the amount of graphite (over the ranges examined), did not strongly influence the fracture toughness. Fracture toughness also did not correlate with tensile properties (i.e. strength or ductility) in these alloys. The results of this work can be used to develop an appropriate quality control program for applications which require assurance against fracture toughness related failures.Nomenclature YS 0.2% offset yield strength (MPa) - UTS Ultimate tensile strength (MPa) - %El % tensile elongation - %RA % reduction in area - E Young's modulus (MPa) - J _Ic Elastic-plastic fracture toughness (fromJ-integral test) (kJ m^–2) - K _Ic Linear-elastic fracture toughness, (MPa m^1/2) - V _v ^graphite Volume fraction graphite - d ^ferrite Ferrite grain size - N _A Nodule count on a random plane (number mm^–2) - D _v Three-dimensional nodule diameter (mm) - _v Three-dimensional mean free nodule spacing (centre-to-centre) (mm) - D _A Average nodule diameter on a random plane (two-dimensional size) (mm) - _A Average nearest neighbour spacing (centre-to-centre) on a random plane (two-dimensional spacing) (mm) - a tog Constants in the multiple linear regression analysis     

Effect of ambient pretreatment of graphite and solvent-catalyst on diamond formation

Diamond was formed from purified natural graphite under high pressure and temperature conditions (7 G Pa, 1700° C) using a solvent-catalyst in the unary (Fe) or binary (Fe-Ti) system. The effect of an ambient pretreatment of the starting mixed powder (graphite and solvent-catalyst) was investigated in relation to the formation and grain growth of diamond. An initial desorption of adsorbed water vapour or harmful gases from the starting powder in vacuum (2 × 10^–5 torr) at higher temperatures (>400° C) was required in order to increase the conversion ratio from graphite to diamond. The subsequent ambient pretreatment at 1000° C in different atmospheres was found to affect the grain growth process of diamond. The depression of grain growth was confirmed in both cases of pretreatments in vacuum (2 × 10^–5 torr) and in an argon atmosphere (1 × 10^–3 or 760 torr). The diamond grains were discrete in the vacuum pretreatment, while a particle joining between the diamond grains was promoted in the argon pretreatment. The pretreatment in an N₂ atmosphere (1 × 10^–3 or 760 torr) tended to accelerate the grain growth of diamond.     

Superfluid onset in4He films adsorbed on pyrolytic graphite

Third-sound velocities and superfluid onsets have been studied for⁴He films adsorbed on pyrolytic graphite. The present onset data are compared with previous experiments on graphite substrates. The third-sound onset data are found to be significantly different from superfluid mass-flow and heat-flow data. A value of 3.19±0.52×10^–9 g cm^–2 K^–1 is obtained for the superfluid areal density at onset divided by the transition temperature. This value is consistent with the Kosterlitz-Thouless-Nelson picture of the phase transition in a two-dimensional superfluid.     

Structure and properties of highly crystallized graphite films based on polyimide Kapton

Highly crystallized graphite films were prepared by heat treatment of carbonized polyimide films (Kapton) at temperatures of 2700 and 3050° C. Interlayer spacing d ₀₀₂ at room temperature, and electrical resistivity, magnetoresistance and Hall coefficient at room and liquid nitrogen temperatures were measured. All of these data indicate high crystallinity of the graphitized Kapton films obtained. For the graphite films heat treated at 3050° C mean-square mobilities were estimated from the magnetoresistance data at 1 T to be 0.91 m² V^–1 sec^–1 at room temperature and 2.3 m² V^–1 sec^–1 at liquid nitrogen temperature; the value at liquid nitrogen temperature corresponds to that for a pyrolytic graphite heat treated at 3200° C for 1 h (PG 3200). Magnetic field dependence of Hall coefficient at liquid nitrogen temperature for this sample also agrees well with that for PG 3200. Scanning electron micrographs on the surfaces show that the present graphite films consist of grains of large crystallites, and grain size increases as the crystallinity of the material improves.     

Production of cast aluminium-graphite particle composites using a pellet method

Copper- and nickel-coated graphite particles can be successfully introduced into aluminium-base alloy melts as pellets to produce cast aluminium-graphite particle composites. The pellets were made by pressing mixtures of nickel- or copper-coated graphite particles and aluminium powders together at pressures varying between 2 and 20 kg mm^–2. These pellets were dispersed in aluminium alloy melts by plunging and holding them in the melts using a refractory coated mild steel cone, until the pellets disintegrated and the powders were dispersed. The optimum pressure for the preparation of pellets was 2 to 5 kg mm^–2 and the optimum size and percentage of aluminium powder were 400 to 1000m and 35 wt% respectively. Under optimum conditions the recovery of the graphite particles in the castings was as high as 96%, these particles being pushed into the last freezing interdendritic regions. The tensile strength and the hardness of the graphite aluminium alloys made using the pellet method are comparable to those of similar composites made using gas injection or the vortex method. The pellet method however has the advantage of greater reproducibility and flexibility. Dispersion of graphite particles in the matrix of cast aluminium alloys using the pellet method increases their resistance to wear.Formerly with Indian Institute of Science, Bangalore, India.     

Influence of Ar ion etching on Tc of liquid-quenched Bi1.6Pb0.4Sr2Ca2Cu3Ox superconductor by sheet plasma source

The influence of argon-ion etching is investigated for liquid-quenched high-T_c Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_x. The argon-ion irradiation has no effect on the T_c value for a dose of 4.05 × 10¹⁷ (ions mm^–2). However, doses in excess of this level greatly decreases the T_c value. Therefore, a critical irradiation does value (D_c) to maintain a T_c value above 100 K is defined and determined. The D_c is about 4.94 × 10¹⁷ (ions mm^–2) for argon-ion irradiation at the low acceleration energy of 1 keV.     

Effect of calcination conditions of self-sintering mesocarbon microbeads on the characteristics of resulting graphite

Mesocarbon microbeads are now-a-days used as a prominent self-sintering precursor for the production of high density monolithic graphite. The quality of this graphite is highly dependent on the characteristics of these microbeads, such as the quinoline and toluene insoluble contents, -resins content and volatile matter content, which in turn, can be controlled to desired values by suitable treatments of their extraction and calcination. In the present paper, the authors give an account of the study conducted to see the effect of calcination conditions of mesocarbon microbeads on the characteristics of the resulting graphite. A calcination at a temperature in the range of 280–320 °C for 30 min. under an ambient pressure of nitrogen, or at a temperature of 245–310 °C for 10 min. under a reduced pressure (5 cm Hg) of nitrogen, results in mesocarbon microbeads having a quinoline insoluble content of 83.6–89.8%, toluene insoluble content of 94.4–99.7%, -resins content of 6.8–11.9% and a volatile matter content of 10.2–13.5%. Such microbeads have been found to lead to a monolithic graphite possessing a bulk density 1.91–2.02 g cm^–3, bending strength of 62–70 MPa, Shore hardness of 58–69, electrical resistivity of 2.1–2.6 m cm and a degree of anisotropy of 1.02–1.05.     

The effect of pretreatment in a fluidized bed upon diamond synthesis on particles by chemical vapour deposition

Diamond synthesis was carried out on non-diamond particles (single- and poly-crystal silicon, quartz and SiC) by microwave plasma-enhanced chemical vapour deposition. Fine diamond particles were deposited on the non-diamond particle surface. The particle deposition density on the untreated particle substrates was strongly dependent on the surface characteristics of the particle substrates. The value ranged from 10–10⁵ mm^–2 for each particle. Particle substrates were pretreated in a gas-solid fluidized bed, and these were then used for the deposition of diamond. The pretreatment of the surface of the particle substrate in the fluidized bed greatly enhanced the nucleation of diamond. A deposition density of about 10⁷ mm^–2 was obtained on single-crystal silicon particles pretreated for 15 h. The effectiveness of the fluidized bed pretreatment on the deposition density was observed to be appreciable for the four kinds of particle examined.     

The peel strengths of diffusion bonded joints between clad Al-alloy sheets

Solid-state diffusion bonded joints were produced between silver-coated clad Al-alloy sheets. The alloys were based upon the systems Al-Zn-Mg (7010 alloy) and Al-Cu (2024 and Supral 220 alloys). The corresponding peel strengths of the joints in these alloys were 61, 45 and 42 N mm^–1 in the solution heat treated state and 34, 12 and 48 N mm^–1 in the aged state. At 480° C corresponding peel strengths were 2.4, 2.5 and 1.7 N mm^–1. The mechanism of peel fracture in the peel test and the possibility of combining diffusion bonding with superplastic forming are discussed.     

Plastic bending of CdxHg1−xTe

Preliminary results are reported of three-point plastic bending tests on Cd _x Hg_1–x Te single crystal samples, for an x value of about 0.2, conducted in air at strain rates of the order of 10^–5 sec^–1, and at temperatures in the range 303 K (30° C) to 363 K (90° C) (in the region of 0.35T _m ⁰ , where T _m ⁰ is the absolute melting point). Single crystal samples were cut from polycrystalline ingots, and the orientation, although measured in each case, was not consistent from sample to sample, being determined by the available grain shape. The stress-strain curves resemble those found for Group IV and III–V semiconductors. They display a yield drop, followed by a region of zero work hardening. All tests were stopped in this region, and in no case did the overall glide strain exceed 3%. The upper and lower yield stresses (outer fibre glide stress values) varied from 16 MN m^–2 and 10 MN m^–2, respectively, at 363 K (90° C) to 24 MN m^–2 and 17 MN m^–2, respectively, at 303 K (30° C).     

Hot dynamic consolidation of hard ceramics

Diamond and cubic boron nitride powders were shock compacted at high temperature (873 and 973 K) by using a planar impact system at 1.2 and 2.0 km s^–1. Silicon, graphite or a mixture of titanium and carbon powders were added to enhance the bonding of these superhard materials. Hot-consolidated specimens exhibited fewer surface cracks as compared with the specimens shock consolidated at room temperature. Diamond compacts having microhardness values over 55 GPa were obtained by subjecting porous mixtures of diamond crystals (4-8 m) plus 15 wt% graphite (325 mesh) to an impact velocity of 1.2 km s^–1 at 873 K. Well-consolidated c-BN samples, with microhardnesses (starting powders with 10–20 and 40–50 (m) over 53 GPa were obtained.     

Nuclear Magnetism of Two Dimensional Solid 3He Adsorbed on Plated Graphite

Nuclear spin exchange in the low density two dimensional quantum solid formed by ³ He adsorbed on graphite plated by a bilayer of HD has been studied by heat capacity and magnetization measurements. The low densities result in a frustrated magnet with significantly larger effective exchange constants than observed in the antiferromagnetic second layer of ³ He on bare graphite. Promotion to a fluid overlayer occurs at 6.8 nm ^–2. A ferromagnetic anomaly is observed in magnetization measurements at 10 nm ^–2 with an effective exchange constant of 1.0 mK, about half the value observed at the corresponding anomaly on bare graphite.     

Preparation of TiB2 sintered compacts by hot pressing

A sintered compact of titanium diboride (TiB₂) was prepared by hot pressing of the synthesized TiB₂ powder, which was obtained by a solid-state reaction between TiN and amorphous boron. Densification of the sintered compact occurred at 20 MPa and 1800° C for 5 to 60 min with the aid of a reaction sintering, including the TiB₂ formation reaction between excess 20 at % amorphous boron in the as-synthesized powder (TiB₂ + 0.2B) and intentionally added 10 at % titanium metal. A homogeneous sintered compact of a single phase of TiB₂, which was prepared by hot pressing for 30 min from the starting powder composition [(TiB₂ + 0.2B) + 0.1 Ti], had a fine-grained microstructure composed of TiB₂ grains with diameters of 2 to 3 m. The bulk density was 4.47 g cm^–3, i.e. 98% of the theoretical density. The microhardness, transverse rupture strength and fracture toughness of the TiB₂ sintered compact were 2850 kg mm^–2, 48 kg mm^–2 and 2.4 MN m^–3/2, respectively. The thermal expansion coefficient increased with increasing temperature up to 400° C and had a constant value of 8.8 x 10^–6 deg^–1 above 500° C.     

Preparation of multilayer targets for g-factor measurement of rotational levels

The three-layer-sandwich targets of ^58,60Ni–Fe–Cu, ¹¹B–Fe–Cu and ^67,68,70Zn–Fe–Au have been prepared for g-factor measurement of rotational levels. The ferromagnetic Fe middle layers of 1.2–1.5 mg/cm² Fe have been made by rolling interrupted by annealing against hardening. Thick recoil stopper layers (5–12 mg/cm²) of Cu and Au on one side of Fe foils have been fabricated by vacuum evaporation. Isotopic Zn, B and Ni layers of 150–400 μg/cm² have been deposited on the opposite side of the Fe foil by electron beam evaporation and focused ion beam sputtering, respectively. For better homogeneity the substrates were rotated.     

X-ray diffraction line profile analysis of nanocrystalline graphite

The structure evolution to nanocrystalline graphite produced by ball milling in n-dodecane has been studied by Fourier analysis of broadened X-ray diffraction line profiles according to double-Voigt method. The Fourier analysis gave size and strain distributions of the coherently diffracting domains (X-ray crystallite size) and root-mean-square-strain (rmss) and their average values. The precursor graphite was defined by average crystal sizes of about hundreds of nanometers, measured along the in-plane and out-of-plane directions, and low rmss value of 0.38 × 10⁻³. During milling, the average crystallite sizes of graphite decreased to about 6 and 43 nm along the out-of-plane and in-plane directions, respectively. Correspondingly, the rmss of milled graphite increased to 6.54 × 10⁻³. Analysis of the out-of-plane to in-plane crystallite size ratios showed that the crystallites became progressively thinner and flatter. A linear relationship between rmss and reciprocal crystallite size along the stacking axis revealed that size of disordered boundary regions gradually increased at the expense of ordered crystalline regions. A model describing crystalline–nanocrystalline transformation of graphite along different crystallographic axis was formulated and used to discuss the experimental data. It was concluded that a distortion-controlled process is responsible for the crystalline–nanocrystalline transformation of graphite milled in n-dodecane.     

Measurements of the temperature rise ahead of a fatigue crack

Summary The temperature rise ahead of a fatigue crack has been measured using a Thermovision camera. Observations were made on three kinds of polymer and an austenitic stainless steel. The maximum temperature difference in macro-scale between the zone ahead of the crack and the bulk of the material was found to be, for the polymers, about 30°C at 725 N/min and amplitude o.1–0.8 kp/mm² and, for the steel, 14°C at 6000 N/min and amplitude 3.0–24.0 kp/mm².     

Preparation and Electrical Properties of Cd<Subscript>x</Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Te Crystals

Single-crystal ingots of Cd_xZn_1−x Te solid solutions are grown by the sublimation method. Samples with x = 0.95, 0.90, and 0.85 taken from the end portions of the ingots are chemically homogeneous and have p-type conductivity with a 300-K hole concentration below 10¹² cm⁻³. Temperature-dependent electrical conductivity measurements are used to evaluate the ionization energies of electrically active centers.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 782–784.Original Russian Text Copyright © 2005 by Britan, Pigur, Popovich, Tsyutsyura.