Direct measurement of the hot carrier cooling rate ina-Si:H using femtosecond 4 eV pulses

For fuel savings as well as energy and resource requirement, high strength low alloy steels (HSLA) are of particular interest to automobile industry because of the potential weight reduction which can be achieved by using thinner section of these steels to carry the same load and thus to improve the fuel mileage. Dual phase treatment has been utilized to obtain superior strength and ductility combinations compared to the HSLA of identical composition. Recently, cooling rate following heat treatment was found to be important to the tensile properties of the dual phase steels. In this paper, we report the results of the investigation of cooling rate on the microstructures and mechanical properties of several vanadium HSLA steels.The steels with composition (in weight percent) listed below were supplied by China Steel Corporation: 1. low V steel (0.11C, 0.65Si, 1.63Mn, 0.015P, 0.008S, 0.084Aℓ, 0.004V), 2. 0.059V steel (0.13C, 0.62S1, 1.59Mn, 0.012P, 0.008S, 0.065Aℓ, 0.059V), 3. 0.10V steel (0.11C, 0.58Si, 1.58Mn, 0.017P, 0.008S, 0.068Aℓ, 0.10V).

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Suppression of γ’ Precipitation in a Laser-Melted Nickel-Base Alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100078870 ◽

1977 ◽

Vol 35 ◽

pp. 270-271

Author(s):

J. M. Walsh ◽

J. C. Whittles ◽

B. H. Kear ◽

E. M. Breinan

Keyword(s):

Cooling Rate ◽

Base Alloy ◽

Material Surface ◽

Intimate Contact ◽

Absorbed Power ◽

Perfect Contact ◽

Nickel Base ◽

Rapidly Solidified ◽

Limiting Case ◽

The Heat Transfer Coefficient

Conventionally cast γ’ precipitation hardened nickel-base superalloys possess well-defined dendritic structures and normally exhibit pronounced segregation. Splat quenched, or rapidly solidified alloys, on the other hand, show little or no evidence for phase decomposition and markedly reduced segregation. In what follows, it is shown that comparable results have been obtained in superalloys processed by the LASERGLAZE™ method.In laser glazing, a sharply focused laser beam is traversed across the material surface at a rate that induces surface localized melting, while avoiding significant surface vaporization. Under these conditions, computations of the average cooling rate can be made with confidence, since intimate contact between the melt and the self-substrate ensures that the heat transfer coefficient is reproducibly constant (h=∞ for perfect contact) in contrast to the variable h characteristic of splat quenching. Results of such computations for pure nickel are presented in Fig. 1, which shows that there is a maximum cooling rate for a given absorbed power density, corresponding to the limiting case in which melt depth approaches zero.

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Voids in Quenched Nickel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100101074 ◽

1968 ◽

Vol 26 ◽

pp. 266-267

Author(s):

J. J. Laidler

Keyword(s):

Electron Beam ◽

Ambient Temperature ◽

Cooling Rate ◽

Three Dimensional ◽

Cooling Curve ◽

Polycrystalline Nickel ◽

Quenching Temperature ◽

Long Tail ◽

Diffusion Pump

The presence of three-dimensional voids in quenched metals has long been suspected, and voids have indeed been observed directly in a number of metals. These include aluminum, platinum, and copper, silver and gold. Attempts at the production of observable quenched-in defects in nickel have been generally unsuccessful, so the present work was initiated in order to establish the conditions under which such defects may be formed.Electron beam zone-melted polycrystalline nickel foils, 99.997% pure, were quenched from 1420°C in an evacuated chamber into a bath containing a silicone diffusion pump fluid . The pressure in the chamber at the quenching temperature was less than 10-5 Torr . With an oil quench such as this, the cooling rate is approximately 5,000°C/second above 400°C; below 400°C, the cooling curve has a long tail. Therefore, the quenched specimens are aged in place for several seconds at a temperature which continuously approaches the ambient temperature of the system.

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