University ’ s repository of research publications and other research outputs The effects of electropulsing on metallic materials Book Chapter
The influence of electropulsing on metallic materials is reviewed, with a focus on phase transformations and grain refinement. While a large and growing body of literature exists on the topic of electropulsing, the mechanisms governing the process are not currently fully understood. Furthermore, the effects of electropulsing on microstructure and mechanical properties are not yet clearly defined. This review seeks to summarise the existing literature in order to highlight and understand research trends across a variety of metals and alloys, and to clarify the state of the art. Research has shown that the electropulsing process is capable of inducing low temperature recrystallisation in metallic materials at an accelerated rate compared to more traditional heat treatment methods. These microstructural changes often alter the mechanical properties of the materials such as ductility, tensile strength and hardness. Crack healing as a result of electropulsing treatment has also been observed in damaged or work hardened materials and pre-deformation of the sample has been shown to enhance the effects of electropulsing.
Electroplastic effect in metals
Abstract : The influence of electric current on the mechanical properties of metals is reviewed. Included are the effects of both low density approx. 1A/sq mm continuous current and high density approx. (1000A/sq mm) current pulses, with special attention given to the latter. The influence of the parameters involved in the thermally-activated overcoming of short-range obstacles to dislocation motion. Considered are: (a) the force drift electrons exert on dislocations held up at obstacles and (b) the influence of drift electrons on the obstacle strength and on the pre-exponential factor. (Author)
Hygroscopic Expansion of some Casting Investments
CREDIT is generally given to Taggart1 for introducing the cast gold inlay to the dental profession. Although he realized that gold shrinks when cooled from molten state to solid state of room temperature, the investment available to him did not supply sufficient compensation. In 1910, Van Horn2 published a paper dealing with a method by which he obtained the compensation by means of wax expansion. The next major research in connection with this problem was the work of Coleman3 at the National Bureau of Standards. He determined the gold shrinkage to be 1.25 per cent and presented a casting technic with compensation values of quantitative nature. The total compensation for the gold shrinkage was obtained by the combination of the setting and thermal expansion of the mold. This procedure is the general practice followed at the present time for compensation. There are some disadvantages to this method. Skinner has indicated the difficulty of obtaining smooth castings and the improper compensation for the casting shrinkage.4 It has been found by Hollenback5 and Scheu6a that castings made at a high temperature are rougher than those made at a low temperature (450° C.), depending upon the great difference in thermal expansion between plaster of Paris and silica, which causes a poor union of the fine particles. This may also result in friability and there may be some warpage due to the differential expansion. A method which provides sufficient compensation at a low mold temperature is the hygroscopic casting technic.b Wilson7 showed that certain plasters expand as much as 0.0044 inch to the inch by taking up moisture from the air. With this information at hand, Scheula, b tested some commercial investment to determine what results the addition of moisture would have. He found6b: (1) All of the casting investments that were tested expanded. (2) The thicker the mix, the greater the expansion. (3) A mix with hot water expanded more than one with cold water. (4) The time at which the mix is placed in the water is of great importance. It was found that if the mix is placed in the water early, it would not expand so much as when placed in a little later. It was also found that if the mix was placed in the water after a certain time, it could not expand to the maximal amount. (5) The temperature of the water in which the mix is placed is important, for two reasons; (a) the temperature of the water controls slightly the expansion of the investment, and (b) water at a temperature of 1000 F. slightly softens the wax pattern so that the fine margins are not marred while expansion is taking place. The mix should remain in the water at least 20 minutes to obtain the full expansion, after which time no further expansion is obtained.