Transition Phase Formation Research Articles

Formation of Transition Phases on Interface between Monocrystalline Fe and Cu Due to Mutual Solid-State Diffusion

Abstract Interdiffusion between Fe (Armco) and Cu single crystals of similar orientation (around [110]) annealed at temperatures of 873 and 973K in air for 0.5 up to 4 h is studied. Formation of three phases different in their chemical composition has been observed: 1) oxide layer on Cu border (porous), 2) a layer rich in copper, iron and oxygen, 3) a layer of iron and oxygen with only small addition of Cu. All reactions of interface formation occurred in solid state. It was noted that oxygen plays an important role in development of new phases. Strong Kirkendall effect is observed due to large difference in diffusion coefficients of copper atoms to iron, DCu→Fe=300exp(-67800/RT) and iron atoms to copper DCu→Fe=0.091exp(-46140/RT).

On the mechanism of enhancing the nucleation behavior of UNCD films by Mo-coating

Enhanced nucleation behavior for ultra-nanocrystalline diamond on Si-substrates via the utilization of Mo-coating was observed. Spectroscopic examinations indicated that the mechanism of enhancement is the formation of Mo 2C phase, which hindered the inward diffusion of carbon species into the substrate materials. The diamonds may either nucleate directly on Mo 2C-layer or via the formation of transition phases, the graphite. The incoming carbons may also react with Mo 2C phase to form MoC phase or form the graphite phase prior to the induction of diamond nuclei. In all cases, the carbons accumulated rapidly due the presence of a Mo 2C (or MoC) layer, triggering the formation of diamond nuclei.

Stress equivalence during early-stage decomposition of Al 1.7 at.% Cu

To supplement X-ray and electron metallography studies during early-stage decomposition, precision activation volumes were determined by strain-rate change technique and stress equivalence between the decrease in the activation volume and the increase in yield stress was found. This result suggests that near-neighbour solute rearrangement in supersaturated random solution initially takes place with multiple-solute obstacles of greater strength to replace single-solute obstacles of higher density prior to the formation of transition phases.

Effect of plastic deformation on the formation and dissolution of transition phases in Al-12 wt.% Mg alloy

Recrystallization, transition phase formation and dissolution of Al-12 wt.% Mg alloy were investigated as a function of the defect density introduced by cold rolling and cold compression deformation. Low and high deformation amounts have been used with the objective that the recrystallization takes place combined with the precipitation reaction to attempt to follow an eventual influence of plastic deformation on the dilatometric curves, the sequence of the precipitation and consequently, on the nature of precipitate particles at determined ageing temperatures. Important anomalies resulting from the plastic deformation appeared in the dilatometric curves, which must be influenced by the recrystallization and the precipitation processes. The latter have never been studied through dilatometric analysis. However, no effect on the precipitation sequence has been observed and it has been confirmed that at relatively high deformation amounts a fine crystalline structure is obtained, while at low deformation amounts a coarser structure is developed. Moreover, it has been shown that the recrystallization does not occur but only the recovery stage is observed. Furthermore, the acceleration effect of plastic deformation on particles nucleation and growth is confirmed.

The influence of Cu and Mg additions on the decomposition of Al-(40 to 50) wt% Zn alloys during isothermal and continuous heating

The influence of 1 wt% copper and 0.2wt% magnesium additions on the heat evolution and structural changes of Al-40 and Al-50wt% Zn alloys during isothermal ageing at 30° C and continuous heating up to 400° C was studied using microcalorimetry, differential scanning calorimetry and transmission electron microscopy. Isothermal studies indicate rapid formation of Guinier-Preston (GP) zones at initial stages of ageing followed by discontinuous precipitation ofβ-phase competing with the formation of transition phases also containing third elements. DSC curves show that the amount of metastable phases formed during room temperature ageing increases with ternary additions, especially to Al-50% Zn alloys. Up to 75° C, GP zones undergo composition but no size changes: during further continuous heating,η' (Mg2Zn) appears, the dissolution of which proceeds parallel to the continuous precipitation ofβ at medium temperatures. Addition of copper reduces the discontinuousβ-precipitation to a lesser extent than magnesium.

Thermodynamic and crystallographic discussion of the formation and dissociation of zircon

The mechanism for the formation of zircon from a system of Si(OC2H5)4-ZrOCl2 · 8H2O-C2H5OH solution was constituted from the following steps; the formation of sol composed of an equimolar Zr4+ located in the neighbourhood of a linear siloxane polymer, deposition of metastable fine (tetragonal) T-ZrO2 by heating, the tetragonal to monoclinic (T → M) transformation of the fine T-ZrO2 aggregates separated from the strain energy of grain boundary between two oxide components, the initiation of the interface reaction between T-ZrO2 and amorphous SiO2, and the acceleration of the formation by the Hedvall effect caused by the crystallization of SiO2. The key technology for the symhesix of zircon from the oxide components ZrO2 and SiO2 was the mechanochemina! activation of the surface layer by milling, the formation of transition phase between the two componems by adding the guest element, and the presentation of metamorphic surface state. Zircon dissociated into M-ZrO2 and SiO2 glass, and the dissociation temperature was expected to be above 1700° C, which required the correction of the phase diagram for ZrO2-SiO2 system used previously.

On the formation of transition phase in AlZn6Mgl alloy

On the formation of transition phase in AlZn6Mgl alloy