Study Of Manufacturing And Characterization Of Metallic Glass Ni-Zr-Al

Transcription

1 Glass and Optical Materials Organized by S.W. Martin, A. Jha, and N.M. Ravindra Materials Science and Technology (MS&T) 2006: MATERIALS AND SYSTEMS - Volume 1 Study Of Manufacturing And Characterization Of Metallic Glass Ni-Zr-Al Meilinda Nurbanasari 1, Djoko Hadiprayitno 2,Irwin Pinayungan 3 1,3 Mechanical Engineering Department; Institute of Technology National; West Java, Indonesia Nuclear Technology Centre of Materials and Radiometri, West Java, Indonesia Key words : Metallic Glass, Amorphous, Glass Transition Temperature Abstract Ni-Zr-Al is one of bulk metallic glass with properties such as strength and elasticity that are far superior to those of conventional metals and also have excellent corrosive-resistance characteristic. The investigations for Ni-Zr-Al especially Zr 60 Al 15 Ni 25 have been conducted for a decade. However, researches for Zr 60 0Al 25 Ni 15, Zr 60 Al 20 Ni 20, and Zr 80 Al 20 are little known. This research aims at comprehend how the microstructure of amorph can be formed, its hardness and determining glass transition temperature (Tg) based on composition of Ni-Zr-Al alloy. The variables used in this research are the temperature of heat treatment, alloy weight, chemical composition, holding time and cooling rate. The manufacturing of Ni-Zr-Al is done through the melting method. This manufacturing is useful to understand the material formation process, as well its microstructures. Test result shows that the microstructure of amorphous alloy is comprised of matrixes and islands. The matrixes contain compound with primary combination, while the islands contain compound impurity substances. The hardness test shows that Ni-Zr-Al, at all composition, owns higher hardness value than Zr-Al compound. The Ni-Zr-Al, as the Al is constantly decreasing at constant Zr, tends to decrease. The value of glass transition temperature, occurred on every sample, can be observed through its physical characteristic changes on the DTA graphical result. Introduction Recently, metallic amorphous alloy is one of the material which has attracted attention of researchers in metallurgy area. [1] With properties such as strength and elasticity that are far superior to those of conventional metals, combined with cheap fabrication, bulk metallic glasses have tremendous potential uses. Although current uses are limited to relatively mundane applications like golf clubs or cell phone casings, the greatest benefit offered by this new material is the possibility of new applications that bulk metallic glass-dependant. Bulk metallic glass is likely to see its greatest successes not in current commercial products, but in future projects where they are the only suitable material to have the products created. [1] All metallic glasses are made up of metal atoms, such as copper, nickel, and titanium. What makes metallic glasses different from ordinary metals is the way in which the atoms are arranged. In 471

2 conventional metal structures, the atoms are arranged in an organized, periodic structure called a crystal. In a glass, including window glass and metallic glass, the atoms are disordered and arranged randomly. The name, metallic glass, signifies a material that is made out of metal atoms that exist in a disordered, glassy state. This unique structure of metallic glass gives interesting and useful properties. Unlike in other metals, the atoms in a metallic glass are not arranged in a crystalline structure. Instead, they are randomly distributed within the material and have no order or structure. This amorphous (non crystalline), or glassy, state is just like the pattern of atoms found in window glass and can loosely be described as a frozen liquid. Because these disorganized atoms do not form crystals, and glass metallic do not have grain boundary and do not know the movement of dislocation [12]. The first form of metallic glass was discovered over forty years ago. In 1960, Pol Duwez and his team found that they could force molten metal to form a glassy instead of crystalline state by cooling the atoms very rapidly. [5,6,11] At that time only very thin ribbons with less than 1 millimeter in thick could be made. In the early 1990s, a major breakthrough accomplished by Inoue et.al with the discovery of a new phenomenon. They found that multi component liquid alloys with very deep eutectics are capable to be frozen to a glassy state several mm to several cm thick by conventional cooling such as in copper die casting [2]. Research Methodology In this research, samples were made for 4 different compositions which consist of Zr, Al and Ni. Zirconium, aluminum and nickel were in form of plate, small block and lump with purity 99.9 %. Composition of alloy was based on weight ratio. Each element and its alloy composition, before and after weighing, are shown in table 1. Table 1 Alloy Composition of Metal Before and After Weighing and based on Weight percentage Composition Sample Alloy (%wt) Ni Zr Al Weight (gr) (%wt) Weight (gr) (%wt) Weight (gr) Total weight (gr) Before after before after before after 1 Ni 15 Zr 60 Al , , , , Ni 20 Zr 60 Al , , , , Ni 25 Zr 60 Al , , , , Ni 80 Al , , ,

3 The steps of this experiment are as follows: M aterial Preparation Zr- A l- N i M aterial cutting & cleaning W eighing : weight total com position of each alloy 20 gr M e ltin g A Etching Sample Testing Ingot cutiing SEM/EDAX Optical microscope DTA As-cast Heat treatm ent (800 C, holding time 1 hour) Quenching (media : liquid nitrogen) Analysis Mounting Conclusion Rough grinding & p o lish in g Hardness testing A Figure 1: The steps of this experiment Melting process uses single arc melting furnace with argon that avoid alloy to oxidize. Examination is conducted to as cast and heat treated sample include microstructure analysis. Specimen is etched by using etchant consist of 250 water 35 ml HNO 3, 21 ml HCl ml and 1 ml HF. [7] Microscopic observation, with optical microscope and chemical composition analysis, is then conducted using SEM-EDAX. Other Examination is hardness test by Micro Vickers, with loading 500 gr and measurement of glass transition temperature use DTA (Differential Thermal Analysis). The increase of temperature is programmed equal to 40 o C/minute. Test Result and Analysis Tables 2 shows the result of material weighing test after melting from every sample Sample Alloy Color Tabel 2 Result of Weighing Test Specimen Weight (gram) Before melting After melting Weight change W before- W after (gram) 1 Ni 15 Zr 60 Al 25 Goldish Yellow Ni 20 Zr 60 Al 20 Goldish Yellow Ni 25 Zr 60 Al 15 Goldish Yellow Ni 80 Al 20 Goldish Yellow

4 Table 2 provides the weight change recorded after melting. It shows the existence of addition and reduction of weight. Weight reduction occurred because the element did not melt altogether. Whilst, the addition of weight occurred as a result of the reaction between metal alloy oxygen gas and other inclusion or because the electrode come into melted metal to become porosity. This phenomenon can be analyzed from the blunt tip of electrode after melting. The result of melting shows that all samples tend to break along in line with freezing process. This occurred because the alloy does not experience shrinkage at the time of freezing process due to alloy s high viscosity. Figure 2 shows the result of hardness. The Data cover the hardness values of heat treated inter metallic compound among metals and non-heat treated ones at various compositions As-Cast Heat Treatment Hardness (VHN) Ni 15 Zr 60 Al Ni 15 Zr 60 Al Ni 15 Zr 60 Al Ni 15 Zr 60 Al composition Figure 2: Relationship between hardness of as-cast and heat-treated materials and its composition. The above figure shows that heat treatment process on each material does not influence hardness value. Materials with composition of Zr 60 Ni 15 Al 25 both for heat-treated and as cast sample have the highest hardness compared to other three compositions. It is visible from the graph that for heat-treated samples, the hardness increases by the increase of Al at constant Zr. While heat-treated and as cast Zr-Al alloys, its hardness decreases significantly. The hardness value of Ni-Zr-Al alloy is relatively homogeneous, while composition number 4, the binary compound of Zr-Al, shows lower hardness value. In general, based on optic microscope observation, it shows that there are islands (Pulau) in the identified matrixes [5]. These islands exist are at all samples. Figure 3 shows microstructure of non heattreated Ni 15 Zr 60 Al 25 alloy. The islands in the matrix look brighter than other areas. The shape is varied, from long, circular, flake, and other forms. Figure 4 generally shows nearly the same appearance as 474

5 figure 3; however its matrix color is paler and not contrast. Here, the islands are still appear in matrix, but it is less in amount and smaller in size. Figure 3 Microstructure of Figure 4 Microstructure of as-cast Ni 15 Zr 60 Al 25 (200x) heat-treated Ni 20 Zr 60 Al 20 (200x) Figure 5 shows more islands and matrixes than sample 1. Those islands are smaller and generally more spherical, flake and also starry form in particular samples. Figure 6 presents smaller and less islands compared to those of in figure 5. The form of the islands varies and showing heterogenous patterns. Figure 5: Microstructure of as-cast Ni 20 Zr 60 Al 20.(200x) Figure 6: Microstructure of heat treated Ni 20 Zr 60 Al 20 at 800 C. (200x) Another samples reflected in Figure 7 shows spherical, acicular, flake and branch islands. While Figure 8 indicates less amount of islands compared to figure 7 with relatively smaller in size. Figure 7 Microstructure of as-cast Ni 25 Zr 60 Al 15. (200x) Figure 8: Microstructure of heat treated Ni 25 Zr 60 Al 15 at 800 C. (200x) 475

6 Figure 9 shows microstructure of alloy Composition of Zr 80 Al 20. In general, the figure shows homogeneous dark colour of samples. It is also visible the occurrence of brighter colour areas which look like islands. From Figure 10 dark matrixes with black spots are seen. Here, islands and matrixes are relatively difficult to distinguish. The amount of islands is still high. Figure 9: Microstructure of as cast Figure 10: Microstructure of heat Zr 80 Al 20. (200x) treated Zr 80 Al 20 at 800 C. (200x) The examination of SEM/EDAX is done to all heat-treated samples, except for Ni 20 Zr 60 Al 20. Both the overall and on spot analysis method are used to each sample. Figure 11 to 13 show the result of SEM for Ni 15 Zr 60 Al 25. Further, the result of EDAX composition test of alloy Ni 15 Zr 60 Al 25 is shown in table 3. Fig 11: Photo of SEM/EDAX by Fig 12:Photo of SEM/EDAX, Fig 13: Photo of SEM/EDAX, over all analysis (M=1000X) at first spot (Matrix). 2500X at second spot (island) Table 3 Composition Analysis of Ni 15 Zr 60 Al 25 Alloy Composition Ni 15 Zr 60 Al 25 Ni Zr Al O S %weight %atom %weight %atom %weight %atom %weight %atom %weight %atom As design 15 13, , , Asheat treated Over all 18,05 17,24 59,80 36,75 22,15 46, First Spot 15,67 14,59 59,91 35,91 24,42 49, Second Spot , ,01-1,23-476

7 Figure 11 shows the overall analysis data with magnification of 1000x. Table 3 shows that the change of chemical composition on sampel 1 after heat treatment is not far different from the early composition before melting. This means that the melting have resulted in homogeneous mixture. From the result analysis of first spot analysis in matrix shown in figure 12, it is seen that the matrix chemical composition consists of primary element compounds. It is also found that element contents in this matrix have the same value as the value of sample 1 composition. At second spot (figure 13), its composition is arranged by other compounds which accidentally entered the melting process. These islands contain number of inclusions like sulphur and oxygen. These inclusions tend to form oxide compounds like SO 3 and ZrO 2. The amount of ZrO 2 compound is relatively high, which equals to %, while SO 3 compound equals to 3.07 %. In this area, the oxygen content is %, sulphur 1.23 % and zirconium % in weight. The aluminium and nickel are not exist here. Figure 14 through 17 show the result of SEM of composition 3 which is heat treated with rapid solidification in liquid nitrogen media. The result of EDAX is shown in table 4. Table 4 shows the result of EDAX test of Ni 25 Zr 60 Al 15 in the percentage of weight and atom by overall and spot analysis. Figure 14 Photo of SEM/EDAX, Ni 25 Zr 60 Al 15, over all analysis 1000x Figure 15 Photo of SEM/EDAX, Ni 25 Zr 60 Al 15, at first spot (matrix) Figure 16 Photo of SEM/EDAX Ni 25 Zr 60 Al 15 at second point (island) Figure 17. Ni 25 Zr 60 Al 15 at third spot (between matrix and island) 477

8 Table 4: Composition Analysis of Ni 25 Zr 60 Al 15 Alloy Composition Ni 25 Zr 60 Al 15 Ni Zr Al O S %weight %atom %weight %atom %weight %atom %weight %atom %weight %atom As design As Heat treated Over all First Spot Second Spot Third Spot Figure 14 shows the result of the overall analysis result of SEM-EDAX with 1000x magnification. It is seen that there are more islands compared to those of in sampel 1. In figure 15, the observation is more focused on matrix area marked by. Here matrixes are the most dominant structure. In general, the matrix consist of a number of primary alloy, which is similar to previous ones. The islands in figure 16, similar to other islands consist of impurity elements, such as oxygen and carbon. The carbon content is % wt or 52% atom, means that the amount of carbon element is very high, even higher than the content of Al and Ni. In figure 17, the alloy structure is spread among matrixes and encircle the islands. Chemical composition test on this area shows almost the same composition as matrixes which composed of Al, Ni and of Zr. In this area, its surface looks is deprived. This happens as a result of the chemical reaction between speciment surface and etchant. Figure 18 through 21 show SEM result of composition Zr 80 Al 20 which has been heat treated with rapid solidification into liquid nitrogen and result of EDAX analysis of Zr 80 Al 20 is shown in table 4. Figure 18: Photo of SEM Zr 80 Al 20 Figure 19: Photo Ni 25 Zr 60 Al 15, Over all analysis (1000x) at first spot (matrix) (2500x) 478

9 Figure 20: Photo of Zr 80 Al 20 at second spot (island) (2500x) Figure 21 Photo of Zr 80 Al 20, at third spot (between matrix and island) (2500x) Table 5 Composition Analysis of Zr 80 Al 20 Alloy Composition Zr 80 Al 20 Zr Al O C %weight %atom %weight %atom %weight %atom %weight %atom As design Over all As-heat treated First spot Second spot Third Spot Figure 18 shows the area taken by overall analysis, it is seen there are number of black spots inside the matrix. Then, data is taken from the first spot, shown in Figure 19. The result of matrix chemical composition shows that composition of Zr and Al is nearly the same as original composition (asdesign). While in Figure 20, the islands contain impuritiy elements; oxygen and carbon. The weight percentage of these impurity elements are relatively high; % of carbon and 8.18 % of oxygen. From the previous analysis, it can be summarized that compounds with impurity element create islands, while intermetallic compounds, composed of number of primary elements, occur in matrixes. DTA Test Result This test is conducted only on heat-treated samples. Table. 6 shows glass transition temperature of heattreated samples. 479

10 Sample Alloy Tabel 6 Result of Differential Thermal Analysis Glass Transition Temperature of Temperature ( C) Crystallization ( C) Remarks 1 Ni 15 Zr 60 Al Amorph 2 Ni 20 Zr 60 Al Amorph 3 Ni 25 Zr 60 Al Amorph 4 Ni 80 Al Crystalline Result of DTA shows that exothermic reaction occurred at every sample. The following figures indicate that when sample is heated from room temperature to 700 o C, it experiences phase transformation reaction. The result of DTA test for each sample can be seen as follows. Figure 22: DTA Curve of heat treated Ni 15 Zr 60 Al 25 (Composition I) at 800 o C Figure 23 Curve DTA heat treated Ni 20 Zr 60 Al 20 (Composition II) at 800 o C Figure 22 indicates that the Ni 15 Zr 60 Al 25 has formed amorph phase. It can be seen from the stable curve signed by the existence of glass transition temperature, at the lower culmination point. After passing this point the curve raises until reaching crystalisation temperature point. The value of this glass transition temperature is o C, while the value of crystalisation temperature is not known. Figure 23 shows the same result as sample 1. The sample has formed amorphous phase but the value of glass transition temperature is different, that is o C and its crystalisation temperature is o C. 480

11 Figrue 24: DTA Curve of Ni 25 Zr 60 Al 15 Figure 25: DTA Curve of Zr 80 Al 20 (composition III) with heat-treated of 800 C. (composition) with heat-treated of 800 C. Figure 24 shows the DTA result for heat treated Ni 25 Zr 60 Al 15 at 800 o C. As the previous sample, this sample has formed amorphous phase with glass transition temperature is o C and crystalisation temperature is o C. Further, the next figure shows glass transition temperature below 0 o C. Thus, before reaching its room temperature, it has formed crystalline. The next sample, sample no. 4 is not amorph but crystalline, possibly the transition phase from to. It is also visible from the graph that there are two curves with 2 minimum points and 2 peak points, which indicates the absence of glass transition temperature. Conclusion From this research, the summaries are as follows: 1. Weight changes occured before and after the melting process, caused by the reaction of oxygen and impurity elements with alloy. The changes might also caused by the dissolved of some electrodes into melted alloy during the melting process. 2. The observation of optic microscope and SEM shows that islands are appeared almost on entire matrix area. Using the EDAX test, it is clear that the islands at all samples are composed of oxide compound, whereas primary compound exist on entire matrixes. 3. From DTA test it is found that every glass compound has different glass transition temperature. The glass transition temperature of sample 4 is not appeared in the graph, because the amorphous phase was not developed. 4. The hardness value of Ni-Zr-Al increases with the addition of Al at constant Zr, while the changes in heat treatment to the samples does not give significantly affect its hardness. 5. The minimum hardness value occurred at sample number 4 (Ni 80 Al 20 ) in both as cast and heattreated samples. 481

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