Spray casting of eutectic ferrous alloys, an alternative to powder metallurgy

In the present study, the effect of microstructure on the wear characteristics of spray cast Al-15Si and Al-20Si alloys has been investigated and compared with that of vertical axis centrifugal cast and chill cast alloys. The spray cast alloys have been subjected to Hot Isostatic Pressing for porosity reduction. HIPing has reduced the porosity in the spray cast Al-15Si and Al-20Si alloys from 19% to 8% and 19% to 2% respectively. The microstructures of spray cast alloys consisted of finely divided globular shaped Si particles with sizes varying from 2–10 µm. The Si particles have been distributed uniformly throughout the Al matrix. On the contrary coarse and segregated microstructures have been observed in vertical axis centrifugal cast and chill cast alloys. The sizes of primary and eutectic Si in vertical axis centrifugal cast alloys are smaller than that in chill cast alloys. The wear rates are the lowest for spray cast alloys and highest for chill cast alloys over a wide range of sliding velocity. The reasons for better wear resistance of spray cast alloys have been discussed in the light of the microstructural features evolved during spray casting.

In the present investigation, the mechanical and wear properties of Al-20Si alloy processed by spray casting and vertical centrifugal casting processes have been evaluated and compared. In spray casting process the melt was gas atomized and the spray-deposited over a copper substrate. The spray-deposit exhibited considerable porosity and subjected to hot isostatic pressing to reduce the porosity from 19 to 2%. The centrifugal casting process provided cylindrical shaped preform with characteristically low porosity. The microstructure of spray cast alloy showed ultra fine and uniformly distributed primary and eutectic Si particles in the Al matrix. In contrast, a coarse polyhedral shaped morphology of the primary Si phase was observed in the microstructure of the centrifugal cast alloy. The wear rate of spray cast alloy was invariably lower than that of centrifugal cast alloy. The room temperature tensile and hardness tests of spray cast alloy showed considerable improvement in its strength, ductility and hardness over that of centrifugal cast alloy. The improvement in wear properties of spray cast alloy is discussed in the light of its microstructural modification induced by spray casting and nature of debris particles generated during wear testing.

In the present study, the microstructural features, wear characteristics, and corrosion behaviour of spray cast Al—12Si, Al—15Si, and Al—20Si alloys have been investigated. The alloys were spray cast and hot isostatically pressed. Hot isostatic pressing has considerably reduced the porosity in spray cast alloys. The microstructure of spray cast alloys showed fine and globular-shaped Si particles in the Al matrix in contrast to needle-type eutectic Si and blocky-type primary Si in the Al matrix in chill cast alloys. The dry sliding wear tests showed that the wear rates of spray cast alloys are invariably lower and the potentiodynamic polarization tests showed that the corrosion resistance of spray cast alloys is considerably higher than that of chill cast alloys. The high wear and corrosion resistance of spray cast alloys have been discussed in the light of the microstructural modification induced during the spray casting process.

Evolution of microstructure and its effect on wear and mechanical properties of spray cast Al–12Si alloy

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Inhibited coarsening of solid-liquid microstructures in spray casting at high volume fractions of solid

Spray casting, also known as spray forming, is a niche casting process for the manufacture of preforms. This article lists commercial examples of alloys manufactured by spray casting and provides sequential steps of the spray casting process. Gas atomization is a chaotic, stochastic process that always produces a wide range of droplet diameters. The article schematically illustrates typical log-normal droplet diameter probability density distribution on a mass or volume basis obtained by gas atomization. It also illustrates the changes in solid fraction during the spray casting process as a function of axial distance from the point of droplet atomization. The article concludes with a section on occurrence of macrosegregation and coarsening in spray cast preforms.

Microstructure and properties of spray cast CuZr alloys

In this study, Cu-10Sn and Cu-10Sn-2Ni-0.2Si alloys have been manufactured by spray casting in order to achieve a fine scale microstructure and high tensile strength, and investigated in terms of microstructural evolution, aging characteristics and tensile properties. Spray cast alloys had a much lower microhardness than continuous cast billet because of an improved homogenization and an extended Sn solid solubility. Spray cast Cu-Sn-Ni-Si alloy was characterized by an equiaxed grain microstructure with a small-sized (Ni, Si)-rich precipitates. Cold rolling of Cu-Sn-Ni-Si alloy increased a tensile strength to 1220 MPa, but subsequent ageing treatment reduced a ultimate tensile strength to 780 MPa with an elongation of 18%.

Comparison of dendrite and dispersive structure in rapidly solidified Cu–Co immiscible alloy with different heat flow modes

Spray cast strip of AISI 1026 and M2 has been produced by the Osprey™ process under controlled conditions of deposition. Droplet flight distance was varied over the range 325 to 475 mm and strip was spray cast onto either planar or roller substrates of copper and steel. Substrate surface speed was in the range of 0.02 to 1 m/s, which produced strip of 0.025 to 0.0007 m thickness, respectively, with a width of 0.1 m. Surface condition, microstructure, and extent of porosity in the strip were characterized as a function of distance from top and bottom surfaces. The microstructure of the strip is comprised of three regions —a ‘chill zone’ at the bottom surface consisting of fine grains of ferrite and pearlite with numerous pores; a middle region containing equiaxed or columnar grains, Widmanstatten plates, and fine pores; and a top region made up of equiaxed grains comprising Widmanstatten plates and a few pores. Process variables of primary importance with respect to microstructural integrity and surface condition of the strip are substrate velocity, the surface condition of the substrate, flight distance, and the uniformity of droplet flux in the spray cone. Flight distance determines the amount of cooling of the droplets by the atomizing gas and, therefore, the average temperature of the spray incident on the substrate. Microstructure is determined by convective cooling of the spray, and, to a lesser extent, by the substrate velocity and temperature. The processing conditions required to spray cast strip with a homogeneous microstructure and uniform thickness/surface condition have been established.

The influence of spray casting technique on martensitic transformation temperature, magnetic properties and compressive properties of Ni50Mn25+xGa25-x (x = 0, 1.25, 2.5, 3.75 and 5) alloys was investigated.With the increase in Mn content, martensitic transformation temperature of the spray casting samples is increased, but slightly lower than that of the corresponding as-cast ones.The saturation magnetization test shows the opposite tendency and proves the spray casting technique can effectively enhance the magnetic properties.Compression experiments showed that the spray casting process did not change the fracture strain, but lead to the greatly increase in the compressive strength and improve the brittleness of the Ni-Mn-Ga alloys.This study may offer a new processing technique for developing high performance ferromagnetic shape memory alloys.

Fracture studies conducted using linear elastic fracture mechanics, crack opening displacement, and J-integral methods have shown that high room temperature toughness can be achieved in plain and low alloyed medium carbon cast steels. The high quality, carefully controlled, and heat treated steels prepared often yielded Jlc values which exceeded 0.1 MPa-m, or Klc values exceeding 150 MPa-m 1/2 Correspondingly, crack tip opening displacement values were of the order of 0.24 to 0.26 mm. Of the several elements examined chromium is the most effective for developing optimum properties at medium carbon levels. However, in general, chemical composition, in terms of major alloying elements, was found to be only a minor variable in determining fracture toughness of the heat treated steel. Fractographic measurements revealed that a squared power relationship exists between the stretched zone width and relative toughness (Klc/Φys) at both low and high toughness levels.

<title/>A kind of low alloy wear resistant cast steel that does not contain costly alloy elements such as molybdenum, nickel, copper and vanadium has been successfully developed. By the refinement with rare earth and titanium, the purification with blowing argon and improving the hardenability with boron, the cast steel containing 0·25-0·45%C, 0·5-1·5%Si, 0·5-1·5%Mn, 0·5-1·5%Cr and a small quantity of titanium, boron, rare earth, calcium and aluminium has high tensile strength, impact and fracture toughness and excellent wear resistance. In the excavator bucket teeth, crusher hammer and ball mill liner, low alloy wear resistant cast steel has 2-4 times longer servicing life than that of Hadfield austenitic steel, and its production cost is equal to that of Hadfield austenitic steel. The use of low alloy wear resistant cast steel is safe and reliable, and there is no fracture and scaling in the use. The application of low alloy wear resistant cast steel has good economic and social benefits.

Cu-Sn based alloys were manufactured by gas atomization spray casting route in order to achieve a fine scale microstructure and a high tensile strength. The spray cast Cu-10Sn-2Ni-0.2Si alloy had an equiaxed grain microstructure, with no formation of brittle <TEX>${\delta}-Cu_{41}Sn_{11}$</TEX> phase. Aging treatment promoted the precipitation of finely distributed particles corresponding to <TEX>${\delta}-Ni_2Si$</TEX> intermetallic phase throughout the <TEX>$\alpha$</TEX>-(CuSn) matrix. The cold-rolled Cu-Sn-Ni-Si alloy had a very high tensile strength of 1200 MPa and an elongation of 5%. Subsequent aging treatment at <TEX>$450^{\circ}C$</TEX> for 1h slightly reduced the tensile strength to 700 MPa and remarkably increased the elongation up to 30%. This result has been explained by coarsening the precipitates due to over aging and reducing the dislocation density due to annealing effects.