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Porosity assessment of suspension and saturated composite castings with the use of microscopic examinations

Staude Marek

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2021

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nr 67 (139)

53--57

EN

Good quality in composite castings can be confirmed primarily by their user. The producer is obliged to create a good product that meets the user’s needs that should undergo quality control. Omission of technological procedures and improper quality control may result in various defects like porosity. This paper presents the characteristics of the casting defect, namely porosity, with a particular focus on porosity in suspension and saturated metal composites. This defect is different, specific to composite castings, making its identification very difficult. The aim of the study is to detect and describe porosity in composites with the use of microscopic and submicroscopic examinations. The assessment of the porosity of the microstructure of composite castings allowed for the formulation of the following conclusions: in addition to the porosity that occurs in castings of classic materials (cast steel, cast iron, and non-ferrous metal alloys), metal composites also distinguish between primary and secondary agglomerates, leaving the reinforcement space not filled, occluded bubbles, and separated gas bubbles.

2

Okluzje gazowe w odlewanych kompozytach nasycanych

Jackowski J.

Kompozyty

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2002

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R. 2, nr 4

180-184

PL

W pracy przedstawiono rozważania na temat powstawania, zachowania się i objętości okluzji w nasycanych odlewach kompozytowych. Powstawanie okluzji w procesie nasycania jest nieuniknione. Gdy na okluzje działa ciśnienie metalostatyczne równe ciśnieniu nasycania zbrojenia, objętość okluzji, zgodnie z równaniem stanu gazów, jest minimalna. W warunkach realnych mogą występować w odlewie kompozytowym wyizolowane obszary (konstrukcja odlewu, warunki jego krzepnięcia), w których ciśnienie wywierane na okluzje może być zdecydowanie niższe, co sprzyja wzrostowi ich objętości. Badania procesu nasycania glinokrzemianowego zbrojenia SIBRAL stopami niskotopliwymi (stop Wooda i stop bezbizmutowy) wykazały, że początkowa objętość okluzji, przy ciśnieniu bliskim normalnemu, wynosi ok. 30%, a porowatość próbek kompozytowych nasycanych stopem Wooda wynosi 2:4% bez względu na sposób ich nasycania. Porowatość próbek nasycanych bezbizmutowym stopem niskotopliwym była zdecydowanie większa. Zbadano rozkład porowatości materiału kompozytowego względem wysokości i średnicy próbek. Stwierdzono, że w przypadku próbek kompozytowych na osnowie stopu Wooda porowatość najbardziej zwartych fragmentów próbek jest równa lub bliska zero. W przypadku osnowy ze stopu bezbizmutowego (skurcz krzepnięcia ok. 2%) najbardziej zwarte fragmenty próbek posiadały 2% porowatość. Przebieg zmian porowatości w wybranych próbkach wskazuje, iż tworzyły się strefy izolowane (na skutek przejmowania nacisku stempla przez zakrzepłe warstwy osnowy), skutkiem czego dekompresja okluzji spowodowała lokalną porowatość materiału kompozytowego o wartości od kilku do kilkunastu procent. Skurcz krzepnięcia osnowy bardzo intensywnie zwiększa porowatość tych fragmentów próbek, które krzepną najpóźniej.

EN

Porosity is highly undesired in any casting, inclusive of composite ones. The paper presents considerations related to formation, behavior, and volume of occlusions in saturated composite castings. Formation of the occlusions during saturation process is inevitable. Assuming the occlusion is subject to metallostatic pressure equal to reinforcement saturation pressure, volume of the occlusion is minimal, in accordance with the equation of gas state. However, under real conditions, such isolated regions may arise within a composite casting (according to easting structure or solidification conditions), in which pressure exerted on the occlusion might be considerably lower (Fig. 1), that induces their volume to increase. Model research of saturation process of an aluminosificate reinforcement SIBRAL with low melting alloys (Wood's alloy or bismuth-free alloy) has shown, that initial occlusion volume, under the pressure approximating its normal value, amounts about to 30%, while porosity of composite samples (diameter40x40 mm) saturated with Wood's alloy amounts to 2:4%, irrespective of the way of their saturation (Fig. 2). Porosity of the samples saturated with bismuth-free low melting alloy was remarkably higher (Tables 1 and 2). Distribution of porosity of composite material has been examined with regard to the height and diameter of the samples (Figs 3 and 4). It was ascertained that for composite samples with Wood's alloy matrix porosity of the most compact parts of the samples is equal to or approximates zero. In case of the Matrix of bismuth-free alloy (solidification shrinkage about 2%) the most compact parts of the samples showed 2% porosity. Variations of porosity in selected samples indicate formation of isolated zones (in result of taking over the pundi pressure by solidified matrix layers). In consequence, decompression of the occlusions resulted in local porosity of the material, reaching a little less than twenty per cent. Solidification shrinkage of the matrix extensively increases porosity of the parts of the samples that solidify latest of all. More careful examination of behavior of the occlusions occurring in saturated composite casting requires metallographic research methods.

3

Analiza mechaniczna recyklingu metalowych kompozytów nasycanych

Nagolska D., Szweycer M.

Kompozyty

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2001

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R. 1, nr 1

35-37

PL

Podjęto próbę analizy procesu recyklingu metalowych kompozytów nasycanych z punktu widzenia zjawisk powierzchniowych. Wnioski wynikające z rozważań teoretycznych potwierdzają przeprowadzone badania. Rozważania mogą być podstawą do dalszych prac związanych z recyklingiem odlewów z tych materiałów.

EN

The paper presents analysis of recycling process of the castings made of metallic saturated composites, with special attention paid to surface phenomena. As the geometry of reinforcement (Fig. 1) is hard or even impossible to describe, the way of filling the reinforcement pore for purposes of theoretical consideration has been assumed according to Fig. 2. Geometrical elements of the pores are shown in Fig. 3. Capillary pressure in the elements may be defined by relationship (1), for the angle a varying from -180° to +180°. The relationship (4) has been derived on the ground of Figures 3 and 4, assuming that x • du1 = du2.The coefficient x may be greater or less than 1. The relationship enables to calculate the pressure in the metal inside the reinforcement. The relationship (4) is shown in Fig. S. Equating it to 0 enabled to determine critical value of the angle Qkr, below which the capillary phenomena are conducive to flowing the metallic matrix out from the reinforcement capillaries. Table 1 shows the conditions and the results of composite recycling trials performed with the view to verifying the theoretical considerations. The research certifies the conclusions drawn from theoretical analysis of the recycling process of castings made of metallic saturated composites: low probability of flowing the liquid matrix out from ceramic reinforcement in air environment, as well as the fact that the better the reinforcement wetting angle with liquid matrix approximates 180°, the greater is the gain of metal derived in recycling process in an artificial e.g. slag environment.