Sigworth Geoffrey K

Bio: Sigworth Geoffrey K is an academic researcher from Cabot Corporation. The author has contributed to research in topics: Alloy & Grain size. The author has an hindex of 6, co-authored 12 publications receiving 496 citations.

The role of boron in the grain

Abstract: It has been known for nearly forty years that the presence of boron in Al-Ti grain refiners has a beneficial effect. Three major theories have been proposed to explain the phenomenon: 1. Boron alters important phase relationships in the Al-Ti-B system. 2. Boron forms TiB2, which is nearly insoluble and acts as an effective nucleus for grain refining. 3. A metastable phase, (Al, Ti)B2, forms and either acts directly as a grain refining agent, or somehow alters the phase relationships as in (1) above. A close examination of these theories, however, shows that none is wholly satisfactory in explaining the experimental evidence. Hence, experimental work was carried out to elucidate further the important role of boron. The (Al, Ti)B2 phase was found to be an effective nucleant in some alloys, in agreement with prior work. In addition, this study suggests that boron may at times improve the grain refining response of Al-Ti alloys by altering the surface structure of TiAl3 nuclei. The mechanisms of grain refinement, therefore, appear to be more complex than has generally been realized.

The Grain Refining of Aluminum and Phase Relationships in the Al-Ti-B System

Abstract: A number of researchers have suggested that there may be phase relationships in the Al-Ti-B system, which can be used to explain why boron improves the grain refining ability of aluminum-titanium master alloys. In this paper, the available information on the phase diagram is reviewed and theoretical calculations are made to establish the ternary Al-Ti-B phase diagram. The phase diagram cannot explain the important effect of boron. It appears to be necessary to seek another explanation.

Study of the mechanism of grain refinement of aluminum after additions of Ti- and B-containing master alloys

Abstract: A highly sensitive thermal analysis technique has been used to study the mechanisms of grain refinement in high-purity aluminum. Additions of Al-Ti-B master alloys were made both below and above the peritectic concentration in reference to the Al-rich corner of the binary Al-Ti phase diagram (0.15 pct Ti in solution). The experiments were conducted at various times after the addition of grain refiner. From the results, except for formation of TiB2, no effect of boron on the Al-rich portion of the binary Al-Ti phase diagram can be observed. With hypoperitectic additions of Al-Ti-B master alloys, TiB2 particles are the most frequent nucleant for aluminum grains. Also, when Al-5Ti-lB additions are made, nucleation frequently occurs above the equilibrium liquidus temperature. From a thermodynamic point of view, this phenomenon can occur only if regions of the melt (which contain bondes and nucleate new grains) have a higher Ti concentration than is present in the bulk of the liquid. A mechanism has been proposed to account for this observation. When hyperperitectic additions of grain refiner were made, a metastable formation of Al solid was often observed to occur at 2 to 5 deg above the equilibrium peritectic temperature. Other researchers have made this observation and proposed that a metastable aluminide phase was formed, even though no X-ray evidence of this phase was found. The experiments reported here show that the metastable nucleation occurs on boride particles when cooling from high temperature, which allow high (metastable) quantities of dissolved Ti to be retained in portions of the melt.

Grain refiner for aluminum containing silicon

Abstract: Disclosed is an Al-Ti-B master alloy especially designed to grain refine cast aluminum alloys containing silicon. The alloy composition goes contrary to present known art. Present commerical master alloys contain a ratio of Ti to B exceeding 2.2 to promote a mixture of TiB2 and TiAl3 crystals. This invention provides an Al-Ti-B alloy wherein the Ti to B ratio is 1. It contains a preponderance of mixed boride crystals. The optimum composition of the alloy of this invention is Al-3Ti-3B.

Aluminum grain refiner containing duplex crystals

Abstract: Disclosed is a new aluminum grain refiner alloy with a controlled, effective content of "duplex" crystals. The duplex crystals are made by (1) producing aluminides that contain boron in solution, and by (2) aging said aluminide in a manner to precipitate at least part of the boron to form the duplex crystals. The duplex crystals have been discovered to be extremely potent grain refining agents.

Grain refinement of aluminium and its alloys by heterogeneous nucleation and alloying

Abstract: Grain refinement of aluminium and its alloys is common industrial practice. The field has been extensively investigated by many workers over the past 50 years, not only to develop efficient grain refiners for different aluminium alloys, but also to achieve an understanding of the mechanism of grain refinement. The present review confines itself to the literature on grain refinement by heterogeneous nucleation and alloying. Initially, the fundamentals of grain refinement by inoculants are outlined. The types of grain refiner, Al-Ti-B master alloys in particular, and their methods of manufacture are next discussed. The grain refining tests to assess the efficiency of the grain refiners and the grain refining behaviour of aluminium alloys are also discussed in brief. The performance of a grain refiner, as well as the response of an aluminium alloy to grain refinement, is influenced by the microstructure of the grain refiner as controlled by the process parameters involved in its preparation and the alloying elements present in the aluminium alloy. The roles of these factors, and particularly the roles of poisoning elements such as Si, Cr, Zr, Li, are reviewed. The paper also reviews the mechanisms of grain refinement, the fading and poisoning phenomena, and the trends in the development of new grain refiners for aluminium alloys containing poisoning elements.

Grain refinement of aluminum alloys: Part I. the nucleant and solute paradigms—a review of the literature

Abstract: Despite the extensive literature on grain refinement, there is not a consensus on the mechanism of grain refinement in aluminum alloys. Recently, there has been a shift in understanding of the grain-refinement paradigm from purely being concerned with the nucleation event, called here the “nucleant paradigm,” to also being concerned with the effect of solute elements, or, the “solute paradigm,” on the final grain structure. This article is divided into two parts. In Part I, the literature underpinning both paradigms is explained, and the validity of the paradigm shift toward the solute paradigm as a more complete understanding of grain refinement is presented. Part II experimentally confirms the validity of the solute paradigm and details a mechanism which explains the need for both effective nucleants and a solute of a good segregating power in order to obtain grain refinement.

Grain refining of aluminium and its alloys using inoculants

Abstract: Grain structure is an important and readily observable feature in cast aluminium alloys. Three different types of grain morphology are possible, namely, columnar, twinned columnar, and equiaxed. Inoculants in the form of master alloys are used to promote the formation of a fully equiaxed grain structure and this is termed grain refinement. Initially, fundamental aspects of solidification are outlined in order that the principles of grain refining using master alloys can be understood. Techniques for the commercial production and testing of common Al–Ti-based master alloys are then discussed briefly. The exact mechanisms by which grain refinement occurs are not yet fully understood and experimental and theoretical studies on the problem are critically reviewed with particular emphasis on (a) the role of solute titanium, (b) the thermodynamics of Al–Ti-based alloy systems, and (c) the nature of heterogeneous nuclei. Finally, current and future trends in the use of grain refining alloys are summarised.

Criteria for developing castable, creep-resistant aluminum-based alloys - A review

Abstract: We describe four criteria for the selection of alloying elements capable of producing castable, precipitation-strengthened Al alloys with high-temperature stability and strength: these alloying elements must (i) be capable of forming a suitable strengthening phase, (ii) show low solid solubility in Al, (iii) low diffusivity in Al, and (iv) retain the ability for the alloy to be conventionally solidified. With regard to criterion (i), we consider those systems forming Al3M trialuminide compounds with a cubic L12 crystal structure, which are chemically and structurally analogous to Ni3Al in the Ni-based superalloys. Eight elements, clustered in the same region of the periodic table, fulfill criterion (i): the first Group 3 transition metal (Sc), the three Group 4 transition metals (Ti, Zr, Hf) and the four latest lanthanide elements (Er, Tm, Yb, Lu). Based on a review of the existing literature, these elements are assessed in terms of criteria (ii) and (iii), which satisfy the need for a dispersion...