Effect of phosphorus on the density and molar volume of Al–Si alloy without solidification shrinkage

The Al–Si alloys exhibit many unique properties, but not enough work has been dedicated to their thermophysical properties. In this work, the effect of phosphorus modifier on the density, molar volume and solidification shrinkage rate of Al-25% Si alloys was investigated by using the indirect Archimedes method. The results show that both density–temperature and molar volume–temperature curves show three inflection points: the liquidus temperature point, the eutectic transformation starting point and the finishing point. The density of the solidus linearly decreases and that of the liquidus linearly increases with phosphorus modifier content. Compared with Vegard’s law, the molar volumes show a negative deviation. Finally, the solidification shrinkage rate is calculated from the densities of solidus and liquidus.

Investigation of the Influence of Ultrasound Action on Diffusion Processes in an Explosion-Welded Bimetal System Cu-Al during Heat Treatment

The influence of ultrasound on the main regularities of the formation and growth of the diffusion zone at the interlayer boundary of an explosion-welded layered composite material of Al-Cu systems is investigated. It is proved that the effect of ultrasound contributes to the reduction of the latent period of the nucleation of intermetallic phases at the interlayer boundary, lowers the temperature of the beginning of the eutectic transformation (by about 10 ° C), but at the same time does not affect the phase composition of the diffusion zone as a result of homogeneous reactions at the boundary of contact of solids. It has been established that the thickness of the diffusion zone, with the duration of the supplied acoustic vibrations, ensures the absence of cracks in the diffusion zone, leading to delamination of the material, increases by 30-40% at a fixed temperature of intense diffusion.

STUDY OF THE FORMATION OF THE STRUCTURE OF GRAY CAST IRON BY THE METHOD OF THERMOGRAPHIC ANALYSIS

The work is devoted to the study of the effect of an exothermic carbon-containing additive of a facing layer of a sandy-clay molding mixture on the eutectic transformation of cast iron. For this, the method of thermographic analysis was used and metallographic analysis of the metal under study was carried out. It is shown that the results obtained by thermographic analysis have a correlation with the structure of cast iron. The introduction of a carbon-containing additive into the composition of the facing mixture led to the formation of a favorable structure of the prototype, characteristic of gray cast iron.

INFLUENCE OF ULTRASOUND ON DIFFUSION ZONE GROWTH KINETICS DURING HEAT TREATMENT OF NICKEL-ALUMINUM BIMETAL

It has been shown experimentally that the effect of ultrasound during heat treatment of the explosion-welded bimetal nickel NP2 + aluminum AD1 helps to reduce the latent nucleation period of NiAl and NiAl intermetallic layers at its interlayer boundary, reduces the temperature of the onset of eutectic transformation (~10 °C), at a temperature of intense diffusion increases the thickness diffusion zone (by 30-40%), without affecting its phase and chemical composition.

Combining Differential Scanning Calorimetry and Cooling-Heating Curve Thermal Analysis to Study the Melting and Solidification Behavior of Al-Ce Binary Alloys

Two common techniques of thermal analysis, Differential Scanning Calorimetry (DSC) and Cooling/Heating Curve Thermal Analysis (CCTA), based on different signal collected and utilizing samples with a weight difference of three orders of magnitude, were used to assess the solidification and melting behavior of Al-Ce binary alloys, containing from 5 to 20 wt. % Ce. Thermal analysis was accompanied by microscopic observations of solidified structures. For heating/cooling rates of 0.2–0.4 °C/s, temperatures of eutectic transformation L ↔ Al + Al11Ce3 in the Al-10Ce alloy along with additional proeutectic reactions L ↔ Al in the Al-5Ce hypoeutectic alloy and L ↔ Al11Ce3 in Al-15Ce and Al-20Ce hypereutectic alloys, were determined. Although there was a general agreement in major transformations, registered by DSC and CCTA during melting and solidification, differences in the reaction temperature determined exceeded the typical measurement errors for each technique. In addition, DSC and CCTA exhibited differences in detecting some proeutectic reactions and minor non-equilibrium effects, accompanying the eutectic transformation. Some factors that could contribute to differences observed and their implications for engineering practice were discussed.

Improvement of mechanical properties of iron castings via adjusting of solidification rate

The work is devoted to improvement of mechanical properties of iron castings via adjusting of the cooling rate without introduction of alloying additives. The new technological solution is suggested; it can be easily adapted to a casting technology. This solution is based on variation of the cooling rate of iron castings within structurally sensitive solidification intervals. For this purpose, the casting mould was initially cooled after pouring, then heated and cooled again. Cooling of the mould during the period of primary austenite crystal forming led to increase of dendrite crystallization rate and was executed using compressed air. Retarding of the cooling rate during the period of eutectic transformation was provided by the mould heating via burning of exothermic carbon-containing additives introduced in a facing layer of sand-clay moulding mix. Burning reaction is accompanied by heat extraction, what steeply retarded the cooling rate within the interval of eutectic transformation. Consequent acceleration of castings cooling within the interval of eutectoid transformation was achieved via repeated air blowing through a worked reaction layer. Adjusted cooling of iron castings allowed to provide the most favourable solidification conditions, taking into account strictly individual requirements for each structurally sensitive temperature intervals. It led to increase of a volumetric part of primary austenite dendrite crystals, to decrease of eutectic transformation overcooling degree, to forming of graphite eutectics and enlargement of dispersity of pearlite component in iron. Consequently, lowering of widespread iron castings rejects takes place, among them chilling, with simultaneous improvement of metal mechanical properties. As a result, the primary and real structures were varied, what had a positive effect on mechanical properties of casting metal. It is shown that use of solidification rate adjustment led to essential increase of metal tensile strength for the experimental casting.

On the Al–Al11Ce3 Eutectic Transformation in Aluminum–Cerium Binary Alloys

The L ↔ Al + Al11Ce3 technologically important eutectic transformation in Al–Ce binary alloys, containing from 5 to 20 wt.% Ce and ranging from hypo- to hypereutectic compositions, was examined along with the microstructure and properties of its solidified product. A combination of thermal analysis and metallography determined the coordinates of the eutectic point at 644.5 ± 0.6 °C and 10.6 wt.% Ce, clarifying the existing literature ambiguity. Despite the high entropy of melting of the Al11Ce3 phase, in hypoeutectic alloys the eutectic was dominated by the regular morphology of periodically arranged lamellae, typical for non-faceted systems. In the lamellar eutectic, however, the faceting of Al11Ce3 was identified at the atomic scale. In contrast, for hypereutectic compositions, the Al11Ce3 eutectic phase exhibited complex morphology, influenced by the proeutectic Al11Ce3 phase. The Al11Ce3 eutectic phase lost its coherency with Al; it was deduced that a partial coherency was present only at early stages of lamellae growth. The orientation relationships between the Al11Ce3 and Al in the eutectic structure, leading to partial coherency, were determined to be [0 0 1]Al ║ [1¯ 1 1]Al11Ce3 with (0 4 4¯)Al ║ (2¯ 0 0)Al11Ce3 and [0 1 1]Al ║ [3¯ 0 1]Al11Ce3 with (2¯ 0 0)Al ║ (0 6 0)Al11Ce3. The Al11Ce3 phase with a hardness of 350 HV and Al matrix having 35 HV in their eutectic arrangement formed in situ composite, with the former playing a role of reinforcement. However, the coarse and mostly incoherent Al11Ce3 eutectic phase provided limited strengthening and the Al–Ce alloy consisting of 100% eutectic reached at room temperature a yield stress of just about 70 MPa.

The structure of alloys of boron-rich corner of Fe–В–C phase diagram

The structure and microdurometric characteristics of the Fe–В–С alloys in the range of high concentration of boron (>16.0 wt. % B) and low concentration of carbon (≥ 0.1 wt. % С) were investigated in this work. The methods of quantitative metallographic, X-ray, differential thermal, fluorescent spectral and microdurometric analyses were applied. Carbon was established to dissolve completely in phase constituents of the investigated alloys, forming solid solutions based on iron borides FeB, FeB2, FeB~4 or FeB~19. It was suggested the existence of one eutectic transformation between borides FeB2 and FeB~4 as well as two peritectic transformations between borides FeB and FeB2 or FeB~4 and FeB~19 correspondingly in the studied concentration range. The formation of boride FeB~4 was explained by its stabilization in the presence of carbon in the alloys. After annealing in vacuum at 900 °C for 10 hours with following quenching, the structure became coarser, but no traces of phase decomposition were revealed in the most alloys. Microhardness of the phases observed in the structure of the investigated alloys increased in the following sequence: FeB→FeB2→FeB~4→FeB~19.

RESEARCH OF THE INFLUENCE OF SLOW-DOWN COOLING SPEED IN THE INTERVAL OF EUTEKTIC TRANSFORMATION ON THE STRUCTURE AND MECHANICAL PROPERTIES OF CAST IRON CASTINGS

The work is devoted to the study of the effect of slowing down the cooling rate in the interval of eutectic transformation on the structure and mechanical properties of castings from gray doeutectic iron. To slow down the cooling rate in the interval of eutectic transformation, an exothermic carbon-containing additive, fuel oil M-100, was used. It is shown that the use of controlled cooling can significantly increase the quality index of cast iron without introducing additional alloying elements into the composition of cast iron.