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Super-alloys for dental welding
M E T A L L O G R A P H Y 9, 193-208 (1976)
193
Super-Alloys for Dental Welding H. PRILUTZKY AND T. PALACIOS Cornision Nacional Energia Atomica, Dto. Metalurgia, Buenos Aires, Argentina
O. RIESGO Centro De Ceramica Dental, Fac. Odontologia, UN BA
The chromium-nickel-based metallic alloys for dental uses were studied by different analytical methods in order to observe their structure and composition. Knowledge of these superalloys will allow one to improve welding techniques with porcelains by controlling their homogeneity level and later diffusion processes.
Introduction The use of chromium-nickel-based metal alloys in porcelain welding for dental prothesis was studied in microprobe analysis carried out earlier [1-]. During these analyses, the interface and neighboring areas were observed with regard to the diffusion of solutes produced in solid condition during the cooling period t h a t follows welding and also during later thermal treatments. Following the same line of investigation, the present paper refers exclusively to the above-mentioned metal alloys. Qualitative and quantitative studies have provided quite a clear knowledge of the metal structure as well as of the distribution of the resulting solutes. Two materials were used, Wiron and Jel-Span. The essential difference observed between these materials lies in the presence of a precious component: palladium in Jel-Span. The presence of a great amount of elements in a variety of alloys makes it difficult to establish their spatial distribution. I t is also difficult to carry out a thorough quantitative analysis, considering that the literature referring to physical and chemical characteristics of Cr-Ni-based alloys refers exclusively, in general, to simple systems [-2-]. Our analysis proved t h a t Ni is in solid solution in Cr and also that different components did vary the melting point: 1380°C for Wiron and 1190°C for Jel-Span. © American Elsevier Publishing Company, Inc., 1976
194
H. Prilutzky, T. Palacios, and O. Ricsgo
Nevertheless, the existing quantity of Cr maintained the typical properties of super alloys such as, first, to provide the materials with a high degree of resistance to oxidation (this fact was proved when no oxides were detected), and second, greater mechanical resistance to high temperature
[-33. Despite the previously mentioned difficulties, a fairly satisfactory concordance was obtained between results and conclusions of analysis made using different techniques: the electron microprobe (CAMECA MS 46 model) on the one hand, and metallographic observations on the other, which gave definitions of the structural characteristics Another difficulty was the lack of information on the thermal treatments applied to each alloy, since it is important to know the history of the material to arrive at some conclusions about mechanical properties, although the knowledge of a microstrueture permits one to foretell fundamental aspects of the material behavior.
Investigation Methods The microprobe was used for qualitative and quantitative analysis. The experimental data were corrected by computer programs with respect to fluorescence, absortion, and atomic number effects [-4]. The C ~ R program was used for both Wiron and Jel-Span cases to correct all analyzed elements. This program, devised by J. Henoc, was adapted from the original, supplied by the National Bureau of Standards F5]. The samples were included in epoxy resin at room temperature, mechanically polished using silicon carbide papers of different granulometry ranging up to 600, and finally finished with diamond paste to obtain a surface without scratches. Previous to insertion into the microprobe, the samples were metallized with a very thin layer of copper so as to improve electric and thermal conductivity and to avoid possible sources of error in the experimental results.
Metallographic Analysis Both analyzed alloys show a dendritic structure which is a consequence of their solidification conditions [-6]. Control of cooling speed and solidification conditions determine the final distribution of the elements present in the alloys that show in their structural complexity a nonhomogeneous chemical composition. Inter-
Dental Materials
195
FIG. 1. Wiron. Enlargement, 200X.
Fro. 2.
Jel-Span. Enlargement, 200 X.
196
H. Prilutzky, T. Palacios, and O. Riesgo
FIG. 3. Jel-Span. Enlargement, 1000X. dendritic spaces are the last to solidify and are richer in solutes than dendritic branches. Also, the interdendritic spaces generally present an inhomogeneous solute distribution characterized by the presence of highly concentrated segregations of one or several solutes and, what is more, an eutectic structure may occur. By employing the metallographic technique it was possible to observe clearly in Wiron as in Jel-Span the previously mentioned structural characteristics, including details present in the alloys. After mechanical polishing and in order to observe the microstructure, the following etching reagents were used: Wiron 25% Nitric acid 75% Chlorhydrie acid 3 sec at room temperature
Jel-Span 50% Glacial acetic acid 50% Nitric acid 7 sec at room temperature
The correct resolution in later photographs was obtained by employing suitable enlargements. I t can be observed in Figs. I and 2 that dendrities in Jel-Span are thinner than those of Wiron. Both cases show the presence of eutectics within interdendritic spaces. For a better resolution in Jel-Span, a greater enlargement is shown in Fig. 3.
197
Dental Materials Results
WIRON The qualitative analysis by means of the microprobe shows a distribution of the existing elements in agreement with results obtained by spectrography as stated in Table 1. Figure 4 shows an electronic image of Wiron alloy in agreement with the micrography of Fig. 1. The alloy's main component, Ni is homogeneously distributed (see Fig 5); chromium, manganese, and molybdenum (Figs. 6, 7, and 8, respectively) are found in dendritic branches although Mn and Mo have segregated between interdendritic spaces. Aluminum (see Fig. 9) presents a segregation similar to that of molybdenum, while silicon shows a strong concentration within interdendritic spaces (Fig. 10). During a punctual analysis carried out on the same scanned area for the previous images, it was also possible to detect small amounts of iron, magnesium, and cobalt, although it was not possible to obtain, as with other elements, the corresponding X images (Fig. 11). Beryllium determined by spectroscopy cannot be detected by electron microprobe, since its atomic number is low and its wavelength large.
TABLE 1 Wiron AlloyAnalysis Analyzed Element
Weight Percentage~
Silicon Aluminium Manganese Cobalt Molybdenum Nickel Chromium Beryllium Iron Magnesium
-4-4-A-t- + A-4-+ q- + A+++ + + -t-
Elements' relative proportion: Up to 1%, + Between 1 and 5%, -t-qOver 5%, +q-q-
198
H. Prilutzky, T. Palacios, and O. Riesgo
FIG. 4. Electronic image (-k) Wiron alloy. 100 X 100 microns.
Fro. 5. Same zone. Xoray image. Ni K~. 100 X 100 microns.
Dental Materials
Fro. 6. Same zone. X-ray image. Cr Ka. 100 X 100 microns.
FIG. 7. Same zone. X-ray image. Mn Ka. 100 X 100 microns.
199
200
H. Prilulzky, T. Palacios, and O. Riesgo
FIG. 8. microns.
Same zone. X-ray image.
Mo L~. 100 X 100
Fro. 9. microns.
Same zone. X-ray image.
A1 K~.
100 X 100
Dental Materials
:FIG. 10. Same zone. X-ray image. Si K.. microns.
201
100 X 100
FIG. 11. Electronic image (-[-). Jel-Span alloy. 200 X 200 microns.
H. Prilutzky, T. Palacios, and O. Riesgo
202
TABLE 2 Wiron Alloy Quantitative Analysis Analyzed Element Silicon Aluminium Manganese Molybdenum Nickel Chromium Cobalt Beryllium
Weight Percentage 0.31 2.04 4.24 2.87 63.89 16.37 10.29~
Iron Magnesium Others These elements were obtained by difference. Although Co, Fe, and Mg were detected, this was only possible within very few zones. Consequently, a correct analysis of the percentages found has no statistical significance. Composition results b y t h e p u n c t u a l q u a n t i t a t i v e analysis m e t h o d after t h e previously m e n t i o n e d corrections were m a d e are shown in T a b l e 2. Because of the heterogeneous distribution of t h e elements, with the exception of nickel the d a t a o b t a i n e d give statistical percentages of the n u m b e r of points considered to c a r r y o u t the analysis. TABLE 3 Jel-Span Alloy Analysis Analyzed Element Silicon Aluminium Manganese Cobalt Molybdenum Nickel Chromium Beryllium Palladium Element's relative proportions: Up to 1%, -4Between 1 and 5%, W-tOver 5 ~ , W-W+
Weight Percentage° W W W W + -4-4--4"4--4--4"4--4-W -4+ ++
Dental Materials
23
JEL-SPAN This alloy (Fig. 11) contains a precious element, palladium. A spectrographic qualitative analysis is given in Table 3. The distribution of main elements observed with the electron microprobe also showed nickel distributed homogeneously (Fig. 12) since the lack of Ni in areas apparently corresponding to dendritic primary branches can be observed. Additional specifications on this matter would lead to speculation. Manganese (Fig. 13) is generally found forming segregations within interdendritic zones; chromium, cobalt, and molybdenum (Figs. 14, 15, and 16, respectively), are distributed within dendrites in a particular way; Mo presents some segregations where Ni is absent, i.e., in dendrites primary branches. Palladium (Fig. 17) shows a distribution within interdendritic spaces. Quantitative analysis results are shown in Table 4. This analysis was also carried out point by point and again the results are an average of the element concentration because of the heterogeneity of the sample.
FIo. 12. Same zone. X-ray image. Ni K~. 200 X 200 microns.
204
H. Prilutzky, T. Palacios, and O. Riesgo
Fro. 13. Same zone. X-ray image. Mn K.. 200 X 200 microns.
Fro. 14. Same zone. X-ray image. Cr K~. 200 X 200 microns.
Dental Materials
FIG. 15. Same zone. X-ray image. Co K~. 200 X 200 microns.
FIG. 16. Same zone. X-ray image. Mo L.. 200 X 200 microns.
205
H. Prilutzky, T. Palacios, and O. Riesgo
206
FIG. 17. Same zone. X-ray image. Pd L~. 200 X 200 microns. The fact that the total percentage exceeds 100% by more or less 1% has no significance, being within the experimental theoretic error accepted in microanalysis techniques [-7].
Comparative Study By observing both alloys it is possible to establish that, although Wiron and Jel-Span present homogeneity in nickel, the existing amount of this element in Wiron almost doubles the quantity in Jel-Span; besides, the proportion of chromium is smaller in Wiron. While cobalt could be perfectly observed in Jel-Span distributed within dendrites, in Wiron it was detected only in small qualtities. Although the presence of palladium in Jel-Span obviously does not inhibit the dendritic structure observed in both cases, it seems to be important for the material properties at the interface formed by the welding couple metal-porcelain [-8]. Another difference was the presence in Wiron of aluminum distributed in some precipitates of interdendritic zones, while in Jel-Span this was not detected.
Dental Materials
207 TABLE 4 Jel-Span Alloy Quantitative Analysis Analyzed Element
Silicon Aluminium Manganese Cobalt Molybdenum Nickel Chromium Palladium
Weight Percentage 0.28 0.04 0.86 11.55 2.40 36.61 25.06 24.21
The experimentally obtained quantitative data were taken at random from a number of X~ points measured during a period of time t sufficient to accumulate a number of counts of statistical significance Ni, corresponding to a normal or Gaussian distribution with a standard deviation equal to the square root of the average [-4J.
Summary As a sequence of this study we feel it is important to point out two fundamental conclusions. The first refers to substructure solidification and the other to composition. Both alloys present a dendritic structure, although spacings are different and differ in the presence of a precious element, Pd. Jel-Span alloy containing Pd is advantageous as regards the quality of metal-porcelain welding, its disadvantage being economic. This gives importance to the second aspect and in that sense the possibility arises of beginning a new investigation based on present knowledge. The investigation should control the solidification conditions of an alloy without Pd as well as the following thermal treatment so as to obtain the utmost possible homogeneous distribution of solutes, since, as observed, the dendritic substructures produce highly fragile areas because their melting point is lower and consequently the material loses cohesion. We therefore point out the importance of investigations aimed at obtaining better-quality chromium-nickel alloys to be applied in the future in porcelain welding dental prothesis.
The author expresses appreciation for the collaboration and contributions given by Ing. H. Espejo and Dr. D. Fainstein, and the Centro de Estudios de Ceramica Dental ( Facultad de Odontologia, Universidad de Buenos Aires)
208
H. Prilutzky, T. Palacios, and O. Riesgo
References 1. O. Riesgo, H. Prilutzky, T. Palacios, UniSn de Aleaciones de Cromo-niquel y Porcelana, Rev. Asoe. Odont. Arg. 60, N ° 7 (July 1972). 2. S.J. Rosemberg, Nickel and its alloys, U.S. Dep. of Commerce. N.B.S. monograph 106 (1968). 3. O. Riesgo, Propiedades mec~nicas de aleaciones de Au y Cr para uso dental, Rev. Asoc. Odont. Arg. 59 (1970). 4. J. Philibert, Modern Analytical Techniques for Metals and Alloys, (J. Busnshah, Ed.) Part 2. 5. J. Henoc, Application du programme COR ~ la microanalyse par sonde ~lectronique, Centre Nat. d'Etudes des Telec. PEC. N ° 61 (1970). 6. B. Chalmers, Principles of Solidification, 1964. 7. D . R . Beaman, J. A. Isasi, Electron beam microanalysis, ASTM Tech. Publication 506 (1972). 8. O. Riesgo, H. Prilutzky, T. Palacios, Interfase Cr-Ni/Porcelana: Pd Rev. Asoc. Odont. Arg. 61, N o 7 (July 1973).
Received March 1975
193
Super-Alloys for Dental Welding H. PRILUTZKY AND T. PALACIOS Cornision Nacional Energia Atomica, Dto. Metalurgia, Buenos Aires, Argentina
O. RIESGO Centro De Ceramica Dental, Fac. Odontologia, UN BA
The chromium-nickel-based metallic alloys for dental uses were studied by different analytical methods in order to observe their structure and composition. Knowledge of these superalloys will allow one to improve welding techniques with porcelains by controlling their homogeneity level and later diffusion processes.
Introduction The use of chromium-nickel-based metal alloys in porcelain welding for dental prothesis was studied in microprobe analysis carried out earlier [1-]. During these analyses, the interface and neighboring areas were observed with regard to the diffusion of solutes produced in solid condition during the cooling period t h a t follows welding and also during later thermal treatments. Following the same line of investigation, the present paper refers exclusively to the above-mentioned metal alloys. Qualitative and quantitative studies have provided quite a clear knowledge of the metal structure as well as of the distribution of the resulting solutes. Two materials were used, Wiron and Jel-Span. The essential difference observed between these materials lies in the presence of a precious component: palladium in Jel-Span. The presence of a great amount of elements in a variety of alloys makes it difficult to establish their spatial distribution. I t is also difficult to carry out a thorough quantitative analysis, considering that the literature referring to physical and chemical characteristics of Cr-Ni-based alloys refers exclusively, in general, to simple systems [-2-]. Our analysis proved t h a t Ni is in solid solution in Cr and also that different components did vary the melting point: 1380°C for Wiron and 1190°C for Jel-Span. © American Elsevier Publishing Company, Inc., 1976
194
H. Prilutzky, T. Palacios, and O. Ricsgo
Nevertheless, the existing quantity of Cr maintained the typical properties of super alloys such as, first, to provide the materials with a high degree of resistance to oxidation (this fact was proved when no oxides were detected), and second, greater mechanical resistance to high temperature
[-33. Despite the previously mentioned difficulties, a fairly satisfactory concordance was obtained between results and conclusions of analysis made using different techniques: the electron microprobe (CAMECA MS 46 model) on the one hand, and metallographic observations on the other, which gave definitions of the structural characteristics Another difficulty was the lack of information on the thermal treatments applied to each alloy, since it is important to know the history of the material to arrive at some conclusions about mechanical properties, although the knowledge of a microstrueture permits one to foretell fundamental aspects of the material behavior.
Investigation Methods The microprobe was used for qualitative and quantitative analysis. The experimental data were corrected by computer programs with respect to fluorescence, absortion, and atomic number effects [-4]. The C ~ R program was used for both Wiron and Jel-Span cases to correct all analyzed elements. This program, devised by J. Henoc, was adapted from the original, supplied by the National Bureau of Standards F5]. The samples were included in epoxy resin at room temperature, mechanically polished using silicon carbide papers of different granulometry ranging up to 600, and finally finished with diamond paste to obtain a surface without scratches. Previous to insertion into the microprobe, the samples were metallized with a very thin layer of copper so as to improve electric and thermal conductivity and to avoid possible sources of error in the experimental results.
Metallographic Analysis Both analyzed alloys show a dendritic structure which is a consequence of their solidification conditions [-6]. Control of cooling speed and solidification conditions determine the final distribution of the elements present in the alloys that show in their structural complexity a nonhomogeneous chemical composition. Inter-
Dental Materials
195
FIG. 1. Wiron. Enlargement, 200X.
Fro. 2.
Jel-Span. Enlargement, 200 X.
196
H. Prilutzky, T. Palacios, and O. Riesgo
FIG. 3. Jel-Span. Enlargement, 1000X. dendritic spaces are the last to solidify and are richer in solutes than dendritic branches. Also, the interdendritic spaces generally present an inhomogeneous solute distribution characterized by the presence of highly concentrated segregations of one or several solutes and, what is more, an eutectic structure may occur. By employing the metallographic technique it was possible to observe clearly in Wiron as in Jel-Span the previously mentioned structural characteristics, including details present in the alloys. After mechanical polishing and in order to observe the microstructure, the following etching reagents were used: Wiron 25% Nitric acid 75% Chlorhydrie acid 3 sec at room temperature
Jel-Span 50% Glacial acetic acid 50% Nitric acid 7 sec at room temperature
The correct resolution in later photographs was obtained by employing suitable enlargements. I t can be observed in Figs. I and 2 that dendrities in Jel-Span are thinner than those of Wiron. Both cases show the presence of eutectics within interdendritic spaces. For a better resolution in Jel-Span, a greater enlargement is shown in Fig. 3.
197
Dental Materials Results
WIRON The qualitative analysis by means of the microprobe shows a distribution of the existing elements in agreement with results obtained by spectrography as stated in Table 1. Figure 4 shows an electronic image of Wiron alloy in agreement with the micrography of Fig. 1. The alloy's main component, Ni is homogeneously distributed (see Fig 5); chromium, manganese, and molybdenum (Figs. 6, 7, and 8, respectively) are found in dendritic branches although Mn and Mo have segregated between interdendritic spaces. Aluminum (see Fig. 9) presents a segregation similar to that of molybdenum, while silicon shows a strong concentration within interdendritic spaces (Fig. 10). During a punctual analysis carried out on the same scanned area for the previous images, it was also possible to detect small amounts of iron, magnesium, and cobalt, although it was not possible to obtain, as with other elements, the corresponding X images (Fig. 11). Beryllium determined by spectroscopy cannot be detected by electron microprobe, since its atomic number is low and its wavelength large.
TABLE 1 Wiron AlloyAnalysis Analyzed Element
Weight Percentage~
Silicon Aluminium Manganese Cobalt Molybdenum Nickel Chromium Beryllium Iron Magnesium
-4-4-A-t- + A-4-+ q- + A+++ + + -t-
Elements' relative proportion: Up to 1%, + Between 1 and 5%, -t-qOver 5%, +q-q-
198
H. Prilutzky, T. Palacios, and O. Riesgo
FIG. 4. Electronic image (-k) Wiron alloy. 100 X 100 microns.
Fro. 5. Same zone. Xoray image. Ni K~. 100 X 100 microns.
Dental Materials
Fro. 6. Same zone. X-ray image. Cr Ka. 100 X 100 microns.
FIG. 7. Same zone. X-ray image. Mn Ka. 100 X 100 microns.
199
200
H. Prilulzky, T. Palacios, and O. Riesgo
FIG. 8. microns.
Same zone. X-ray image.
Mo L~. 100 X 100
Fro. 9. microns.
Same zone. X-ray image.
A1 K~.
100 X 100
Dental Materials
:FIG. 10. Same zone. X-ray image. Si K.. microns.
201
100 X 100
FIG. 11. Electronic image (-[-). Jel-Span alloy. 200 X 200 microns.
H. Prilutzky, T. Palacios, and O. Riesgo
202
TABLE 2 Wiron Alloy Quantitative Analysis Analyzed Element Silicon Aluminium Manganese Molybdenum Nickel Chromium Cobalt Beryllium
Weight Percentage 0.31 2.04 4.24 2.87 63.89 16.37 10.29~
Iron Magnesium Others These elements were obtained by difference. Although Co, Fe, and Mg were detected, this was only possible within very few zones. Consequently, a correct analysis of the percentages found has no statistical significance. Composition results b y t h e p u n c t u a l q u a n t i t a t i v e analysis m e t h o d after t h e previously m e n t i o n e d corrections were m a d e are shown in T a b l e 2. Because of the heterogeneous distribution of t h e elements, with the exception of nickel the d a t a o b t a i n e d give statistical percentages of the n u m b e r of points considered to c a r r y o u t the analysis. TABLE 3 Jel-Span Alloy Analysis Analyzed Element Silicon Aluminium Manganese Cobalt Molybdenum Nickel Chromium Beryllium Palladium Element's relative proportions: Up to 1%, -4Between 1 and 5%, W-tOver 5 ~ , W-W+
Weight Percentage° W W W W + -4-4--4"4--4--4"4--4-W -4+ ++
Dental Materials
23
JEL-SPAN This alloy (Fig. 11) contains a precious element, palladium. A spectrographic qualitative analysis is given in Table 3. The distribution of main elements observed with the electron microprobe also showed nickel distributed homogeneously (Fig. 12) since the lack of Ni in areas apparently corresponding to dendritic primary branches can be observed. Additional specifications on this matter would lead to speculation. Manganese (Fig. 13) is generally found forming segregations within interdendritic zones; chromium, cobalt, and molybdenum (Figs. 14, 15, and 16, respectively), are distributed within dendrites in a particular way; Mo presents some segregations where Ni is absent, i.e., in dendrites primary branches. Palladium (Fig. 17) shows a distribution within interdendritic spaces. Quantitative analysis results are shown in Table 4. This analysis was also carried out point by point and again the results are an average of the element concentration because of the heterogeneity of the sample.
FIo. 12. Same zone. X-ray image. Ni K~. 200 X 200 microns.
204
H. Prilutzky, T. Palacios, and O. Riesgo
Fro. 13. Same zone. X-ray image. Mn K.. 200 X 200 microns.
Fro. 14. Same zone. X-ray image. Cr K~. 200 X 200 microns.
Dental Materials
FIG. 15. Same zone. X-ray image. Co K~. 200 X 200 microns.
FIG. 16. Same zone. X-ray image. Mo L.. 200 X 200 microns.
205
H. Prilutzky, T. Palacios, and O. Riesgo
206
FIG. 17. Same zone. X-ray image. Pd L~. 200 X 200 microns. The fact that the total percentage exceeds 100% by more or less 1% has no significance, being within the experimental theoretic error accepted in microanalysis techniques [-7].
Comparative Study By observing both alloys it is possible to establish that, although Wiron and Jel-Span present homogeneity in nickel, the existing amount of this element in Wiron almost doubles the quantity in Jel-Span; besides, the proportion of chromium is smaller in Wiron. While cobalt could be perfectly observed in Jel-Span distributed within dendrites, in Wiron it was detected only in small qualtities. Although the presence of palladium in Jel-Span obviously does not inhibit the dendritic structure observed in both cases, it seems to be important for the material properties at the interface formed by the welding couple metal-porcelain [-8]. Another difference was the presence in Wiron of aluminum distributed in some precipitates of interdendritic zones, while in Jel-Span this was not detected.
Dental Materials
207 TABLE 4 Jel-Span Alloy Quantitative Analysis Analyzed Element
Silicon Aluminium Manganese Cobalt Molybdenum Nickel Chromium Palladium
Weight Percentage 0.28 0.04 0.86 11.55 2.40 36.61 25.06 24.21
The experimentally obtained quantitative data were taken at random from a number of X~ points measured during a period of time t sufficient to accumulate a number of counts of statistical significance Ni, corresponding to a normal or Gaussian distribution with a standard deviation equal to the square root of the average [-4J.
Summary As a sequence of this study we feel it is important to point out two fundamental conclusions. The first refers to substructure solidification and the other to composition. Both alloys present a dendritic structure, although spacings are different and differ in the presence of a precious element, Pd. Jel-Span alloy containing Pd is advantageous as regards the quality of metal-porcelain welding, its disadvantage being economic. This gives importance to the second aspect and in that sense the possibility arises of beginning a new investigation based on present knowledge. The investigation should control the solidification conditions of an alloy without Pd as well as the following thermal treatment so as to obtain the utmost possible homogeneous distribution of solutes, since, as observed, the dendritic substructures produce highly fragile areas because their melting point is lower and consequently the material loses cohesion. We therefore point out the importance of investigations aimed at obtaining better-quality chromium-nickel alloys to be applied in the future in porcelain welding dental prothesis.
The author expresses appreciation for the collaboration and contributions given by Ing. H. Espejo and Dr. D. Fainstein, and the Centro de Estudios de Ceramica Dental ( Facultad de Odontologia, Universidad de Buenos Aires)
208
H. Prilutzky, T. Palacios, and O. Riesgo
References 1. O. Riesgo, H. Prilutzky, T. Palacios, UniSn de Aleaciones de Cromo-niquel y Porcelana, Rev. Asoe. Odont. Arg. 60, N ° 7 (July 1972). 2. S.J. Rosemberg, Nickel and its alloys, U.S. Dep. of Commerce. N.B.S. monograph 106 (1968). 3. O. Riesgo, Propiedades mec~nicas de aleaciones de Au y Cr para uso dental, Rev. Asoc. Odont. Arg. 59 (1970). 4. J. Philibert, Modern Analytical Techniques for Metals and Alloys, (J. Busnshah, Ed.) Part 2. 5. J. Henoc, Application du programme COR ~ la microanalyse par sonde ~lectronique, Centre Nat. d'Etudes des Telec. PEC. N ° 61 (1970). 6. B. Chalmers, Principles of Solidification, 1964. 7. D . R . Beaman, J. A. Isasi, Electron beam microanalysis, ASTM Tech. Publication 506 (1972). 8. O. Riesgo, H. Prilutzky, T. Palacios, Interfase Cr-Ni/Porcelana: Pd Rev. Asoc. Odont. Arg. 61, N o 7 (July 1973).
Received March 1975