- Email: [email protected]
Use of small punch test to estimate the mechanical properties of sintered products and application to synchronizer hubs
Metal Powder Report Volume 00, Number 00 March 2016
metal-powder.net
SPECIAL FEATURE
Use of small punch test to estimate the mechanical properties of sintered products and application to synchronizer hubs M. Ferna´ndez1, C. Rodrı´guez2, F.J. Belzunce2 and T.E. Garcı´a2 1 2
PMG Fu¨ssen GmbH, Hiebelerstr. 4, 87629 Fu¨ssen, Germany SIMUMECAMAT, University of Oviedo, Edificio Departamental Oeste 7.1.17, Campus Universitario, 33203 Gijo´n, Spain
Powder metallurgy is a manufacturing technology widely used, especially in the automotive sector. In order to assure the quality of these components different conventional tests are employed directly on the final product, but in order to make the mechanical characterization of sintered materials, standard mechanical tests can only be performed onto samples compacted and sintered in controlled conditions similar to the ones used in real production. The final mechanical properties of these products after compacting and sintering are the input needed to define and analyze new geometries and products. The use of the small punch test (SPT) to mechanically characterize in a direct way the final sintered products was explained in this research work and the regressions to determine the tensile mechanical properties of the aforementioned products were also developed.
Introduction The SPT is a very useful test in many occasions, for example when the mechanical part to be characterized is small and it is impossible to use a standard test, as the tension test. The SPT uses small-sized specimens (10 mm 10 mm and 0.5 mm thick) who are firmly clamped between two circular dies and are biaxially strained until failure into a circular hole using a hemispherical punch (Fig. 1). The ‘load-punch displacement’ record can be used to estimate the yield strength [1–6], the ultimate tensile strength [1,3–6] and the tensile elongation [3]. Fig. 2 shows the typical plot of the load versus punch displacement of a ductile metallic alloy with different zones marked on it. In the limit of zone I and II, we can obtain the Py load, which divided by the square of the specimen initial thickness (t) gives us the material yield strength (sys), through a linear relationship (Eq. (1)). Moreover, it is possible to obtain the tensile strength (sut) and the tensile elongation (A) from the load (Pm) and displacement (dm), respectively, obtained at the maximum load
E-mail address: [email protected].
point of the graph. Typical relationships between these parameters are [1,3–6]: s ys ¼ a1 c_
Py þ a2 t2
(1)
s ut ¼ b1 c_
Pm þ b2 t2
(2)
Að%Þ ¼ g 1 c_
dm þ g2 t
(3)
where a1, a2, b1, b2, g1, g2, are constants. The aim of this work was to evaluate the applicability of the SPT to estimate the mechanical properties of powder metallurgy products used in the automotive industry. To achieve this target, the characteristic curve of the SPT for these materials was analyzed, extracting the characteristic values of load and displacement. Then, these values were compared with parameters obtained from conventional tensile tests to ascertain whether there is any correlation between them. Finally, these relationships were used to estimate the mechanical properties of commercial synchronizer hubs used in vehicle gearboxes.
0026-0657/ß 2016 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mprp.2016.02.056
1 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
MPRP-580; No of Pages 6 SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 March 2016
SPECIAL FEATURE
FIGURE 1
Tensile and small punch test correlations Materials The correlations were analyzed using three different commercial powders: Mat1, a diffusion-bonded powder of nominal composition Fe–0.5Mo–1.5Cu–4.0Ni and 0.5% graphite; Mat2, a prealloyed/diffusion-alloyed powder of nominal composition Fe–1.4Mo–2.0Cu–4.0Ni and 0.6% graphite; and Mat3, a prealloyed Fe–3Cr–0.5Mo and 0.45 graphite. Prismatic samples of (120 mm 30 mm 15 mm) were cold pressed at 600 MPa. The samples corresponding to Mat1 and Mat2 were double-pressed and double-sintered: presintered at 800 8C for 45 min in furnace under a N2/H2 atmosphere, repressed to a density around 7.0–7.1 g/cm3 and finally sintered for 30 min in a belt furnace at 1135 8C under endogas. Mat3 samples were pressed to an average density of 6.95– 6.98 g/cm3 and sintered for 45 min in a roller furnace at 1135 8C under a 90N2–10H2 atmosphere. Finally, 50% of the samples were tempered for 45 min at 180 8C. The different specimens (tensile and SPT) were machined from the prismatic samples showed in Fig. 3a and their geometry and situation are summarized in Fig. 3b. Tensile specimens had a width of 4 mm, thickness of 0.5 mm thick and a gauge length of 25 mm. Knowing the influence of porosity on the mechanical properties of these materials, two different thickness locations were analyzed (mid-thickness and surface, m and s respectively).
FIGURE 2
FIGURE 3
The carbon content, evaluated on both surfaces of the different samples, using a standard Leco analyzer, is summarized in Table 1. This table also shows the HB2.5 hardness of all the samples measured according to DIN 30910 (Part 4) and the density results, according to ISO 2738:2000. The porosity was measured by using image analysis techniques. An optical microscope Nikon Epiphot 200 was employed. It was connected to an image analyser provided with a Buehler Entreprise Omnimet software, with a standard error of 0.1%. The porosity value was obtained as the average of the measurements of 5 images per zone with a 100 magnification. It is reasonable to think that the variability of mechanical properties typical of this kind of materials, may be due to porosity differences among the specimens. In fact, a thorough analysis of these samples has shown significant porosity differences, as it is also reflected in Table 1. In the mid-thickness region (m), porosity is always larger than in the both surface (m versus s1 and s2), as a consequence of pressure heterogeneity along the vertical direction. Table 1 gathers all these porosity values. It is highlighted that significant porosity differences among the different locations were
2 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
MPRP-580; No of Pages 6 Metal Powder Report Volume 00, Number 00 March 2016
SPECIAL FEATURE
SPECIAL FEATURE
TABLE 1
FIGURE 5
measured and this fact can explain differences on the measured mechanical properties
Tensile and small punch test: analysis of correlations Tensile specimens were tested according to DIN-EN-10002-1 in an Instron testing machine at a crosshead speed of 1 mm/min. SPT specimens had a standard geometry (10 mm 10 mm 0.5 mm) and were tested using the experimental device depicted in Fig. 1, mounted on a universal testing machine with a load cell of 5 kN. A punch diameter of 2.5 mm, a hole in the lower die with a diameter of 4 mm (provided by a 0.2 mm corner radius) and a displacement rate of 0.2 mm/min were used in all these tests. The brittle behavior of PM materials, well known through tensile tests, and mainly based on their porosity, was confirmed by the obtained SPT curves and by the type of failure characteristic of such samples (star cracking), and this fact also explains the high variability of their mechanical strengths, as it was demonstrated on previous works. Fig. 4 shows the characteristic SPT curves of a
FIGURE 4
ductile structural steel along with another one corresponding to a PM material used in a previous work. After a predominantly elastic zone and a slight plastification, the slope of the PM curve clearly decreases until final failure. In the case of sintered materials, being the load at onset of plastification (Py in Fig. 2) and the one corresponding to final failure (Pm in Fig. 2) so close, the correlations of the SPT resistant parameters (Py/t2 and Pm/t2) and the tensile ones are the same (expressions (4) and (5)). Fig. 4 also shows the typical ‘‘star failure’’ pattern obtained with PM materials in the SP tests. This pattern is characteristic of brittle materials (the typical SPT circumferential ductile failure is also shown in the same figure). Figs. 5 and 6 show, respectively, the tensile test and SPT curves obtained with the specimens extracted at mid-thickness (m) of the different samples. The parallelism of the results obtained with both type of tests is remarkably. Table 2 summarizes the average values and the standard deviation of both tensile and SPT parameters obtained with all materials and treatments at the different locations (near surface, s and midthickness, m).
FIGURE 6
3 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
MPRP-580; No of Pages 6 SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 March 2016
TABLE 2
SPECIAL FEATURE
The influence of the specimen location along the Z axis (Zs versus Zm) is worth to be highlighted. The mid-thickness specimens show in general lower strength and ductility than the specimens located near the sample surface. These facts can be explained, first due to the larger cooling rate suffered by the sample surface (microstructure with a higher strength [7]) and also because the porosity is larger in the center of the compacted and sintered samples, as it was already shown in Table 2 [8]. Figs. 7–9 show the correlations obtained between the tensile mechanical properties and the corresponding SPT parameters. The obtained regressions are quite good and, in the case of the yield and ultimate strengths, the obtained expressions are identical, due to the closeness of both points in both SPT and tensile test, as it was previously explained. Fig. 10 shows the values Py/t2 versus sys obtained in this work together with the obtained by Garcı´a et al. [9] using many different metallic materials. This figure also
FIGURE 7
FIGURE 8
FIGURE 9
4 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
MPRP-580; No of Pages 6 Metal Powder Report Volume 00, Number 00 March 2016
SPECIAL FEATURE
FIGURE 10
shows the Pm/t2 versus sut values also obtained in this work. We can appreciate that all the points can be adjusted by a linear regression with the same slope: s ys ¼ 0:343
Py t2
(4)
aut ¼ 0:343
Pm t2
(5)
Finally, Fig. 9 shows the correlation between the dm/t parameter obtained in the SPT test and the tensile elongation. Expression (6) describes this correlation Að%Þ ¼ 2:5387
dm þ 1:41 t
(6)
Verification using new synchronizer hubs In order to study the accuracy of the mentioned correlations (expressions (4), (5) and (6)) and the influence of porosity on the mechanical properties of sintered material, new tests were carried out using commercial synchronizer hubs produced with a diffusion-bonded commercial powder of nominal composition Fe–0.5Mo–1.5Cu–4.0Ni (0.5% graphite and 0.8%wax). The
FIGURE 11
samples were double-pressed and double-sintered: repressed to a density between 7.0 g/cm3 and 7.1 g/cm3 and finally sintered for 30 min in a belt furnace at 1135 8C under an endogas atmosphere (SYH1 samples). Finally, 50% of the synchronizer hubs were tempered at 180 8C for 45 min (SYH2 samples). Fig. 11 shows the geometry of the analyzed synchronized hubs. Tensile and SPT specimens were extracted from the three sectors of the hubs at the locations and orientations shown in Fig. 5 (this figure only shows the extraction made on a single sector of the component). Tensile specimens 4 mm wide, 0.5 mm thick and with a gauge length of 25 mm were tested according to DIN-EN10002-1 in an Instron testing machine at a crosshead speed of 1 mm/min. standard SPT specimens were extracted in the same positions than tensile ones. Moreover, the average porosity of the three sectors of the synchronizer hub was also metallographically measured using image analysis. Table 3 summarizes the tensile test properties obtained in the different sectors of the analyzed synchronizer hubs along with their respective porosities. The obtained results (tensile parameters and porosity) are quite homogeneous and an average porosity of 6.25% was determined. It is also worth to mention the slight improvement of the resistant properties (elastic modulus and yield and tensile strengths) after tempering. By the contrary, tempering does not seem to affect ductility. The homogeneity observed in the tensile tests was also a feature characteristic of the small punch results. Fig. 12 shows the SPT curves obtained with samples machined from the different sectors of the SYH2 (curves have been corrected using the original sample thickness). Table 4 summarizes the average values and the standard deviation of the SPT parameters obtained with samples machined from
FIGURE 12
5 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
SPECIAL FEATURE
TABLE 3
MPRP-580; No of Pages 6 SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 March 2016
SPECIAL FEATURE FIGURE 13
TABLE 4
SPT specimens in cases where samples have a same amount of porosity. Finally, it is worth to highlight again the utility of the SPT methodology to carry out the mechanical characterization of PM products.
Conclusions
the different sectors of all the analyzed synchronizer hubs. Moreover, Table 4 shows the values of porosity obtained in the different analyzed sectors. We can see the high homogeneity of the porosity values and how this is reflected in the low dispersion of the SPT parameters. In addition, these porosity values are very similar to those obtained in the tensile specimens (Table 3). Fig. 13 shows the correspondence between the SPT resistant parameters (Py/t2, Pm/t2) and the tensile ones (sy and su) obtained in this work along with the results obtained in previous works [9]. As can be seen, the values obtained in this work lie within the typical dispersion range showed for a great number of different metallic materials. Furthermore, the fact that the correlation points obtained in this work lie above the average straight line may be related with the low porosity of the hub samples, opening the door to a better prediction of their mechanical properties using
The applicability of the small punch test to mechanically characterize powder metal products has been demonstrated and valid correlations have been proposed in order to obtain their tensile mechanical properties from the typical SPT parameters. By means of the proposed correlations, the tensile properties of sintered products manufactured using three different powders were determined and also the mechanical properties at different locations of synchronizer hubs. Moreover, the benefits of applying a tempering treatment at the final product are also worth to be remarked. References [1] [2] [3] [4] [5] [6] [7]
M. Suzuki, M. Eto, K. Fukaya, et al. J. Nucl. Mater. 179–181 (1991) 441–444. D. Finarelli, M. Roedig, F. Carsughi, J. Nucl. Mater. 328 (2004) 146–150. C. Rodrı´guez, J. Garcı´a, E. Ca´rdenas, C. Betego´n, Weld. J. 88 (2009) 188–192. X. Mao, H. Takahashi, J. Nucl. Mater. 150 (1987) 42–52. E. Fleury, J.S. Ha, Int. J. Pres. Ves. Pip. 75 (1998) 699–706. Y. Ruan, P. Spa¨tig, M. Victoria, J. Nucl. Mater. 307–311 (2002) 236–239. Influence of microstructure and porosity on fatigue properties of sintered steels, B. ¨ gana¨s AB, Ho ¨ gana¨s Sweden. Lindqvist, Ho ¨ gana¨s AB, Sweden, 1967. [8] BOCKSTIEGEL, G., Unpublished data held by Ho [9] T.E. Garcı´a, C. Rodrı´guez, F.J. Belzunce, C. Sua´rez, J. Alloys Compd. 582 (2014) 708–717.
6 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
metal-powder.net
SPECIAL FEATURE
Use of small punch test to estimate the mechanical properties of sintered products and application to synchronizer hubs M. Ferna´ndez1, C. Rodrı´guez2, F.J. Belzunce2 and T.E. Garcı´a2 1 2
PMG Fu¨ssen GmbH, Hiebelerstr. 4, 87629 Fu¨ssen, Germany SIMUMECAMAT, University of Oviedo, Edificio Departamental Oeste 7.1.17, Campus Universitario, 33203 Gijo´n, Spain
Powder metallurgy is a manufacturing technology widely used, especially in the automotive sector. In order to assure the quality of these components different conventional tests are employed directly on the final product, but in order to make the mechanical characterization of sintered materials, standard mechanical tests can only be performed onto samples compacted and sintered in controlled conditions similar to the ones used in real production. The final mechanical properties of these products after compacting and sintering are the input needed to define and analyze new geometries and products. The use of the small punch test (SPT) to mechanically characterize in a direct way the final sintered products was explained in this research work and the regressions to determine the tensile mechanical properties of the aforementioned products were also developed.
Introduction The SPT is a very useful test in many occasions, for example when the mechanical part to be characterized is small and it is impossible to use a standard test, as the tension test. The SPT uses small-sized specimens (10 mm 10 mm and 0.5 mm thick) who are firmly clamped between two circular dies and are biaxially strained until failure into a circular hole using a hemispherical punch (Fig. 1). The ‘load-punch displacement’ record can be used to estimate the yield strength [1–6], the ultimate tensile strength [1,3–6] and the tensile elongation [3]. Fig. 2 shows the typical plot of the load versus punch displacement of a ductile metallic alloy with different zones marked on it. In the limit of zone I and II, we can obtain the Py load, which divided by the square of the specimen initial thickness (t) gives us the material yield strength (sys), through a linear relationship (Eq. (1)). Moreover, it is possible to obtain the tensile strength (sut) and the tensile elongation (A) from the load (Pm) and displacement (dm), respectively, obtained at the maximum load
E-mail address: [email protected].
point of the graph. Typical relationships between these parameters are [1,3–6]: s ys ¼ a1 c_
Py þ a2 t2
(1)
s ut ¼ b1 c_
Pm þ b2 t2
(2)
Að%Þ ¼ g 1 c_
dm þ g2 t
(3)
where a1, a2, b1, b2, g1, g2, are constants. The aim of this work was to evaluate the applicability of the SPT to estimate the mechanical properties of powder metallurgy products used in the automotive industry. To achieve this target, the characteristic curve of the SPT for these materials was analyzed, extracting the characteristic values of load and displacement. Then, these values were compared with parameters obtained from conventional tensile tests to ascertain whether there is any correlation between them. Finally, these relationships were used to estimate the mechanical properties of commercial synchronizer hubs used in vehicle gearboxes.
0026-0657/ß 2016 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mprp.2016.02.056
1 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
MPRP-580; No of Pages 6 SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 March 2016
SPECIAL FEATURE
FIGURE 1
Tensile and small punch test correlations Materials The correlations were analyzed using three different commercial powders: Mat1, a diffusion-bonded powder of nominal composition Fe–0.5Mo–1.5Cu–4.0Ni and 0.5% graphite; Mat2, a prealloyed/diffusion-alloyed powder of nominal composition Fe–1.4Mo–2.0Cu–4.0Ni and 0.6% graphite; and Mat3, a prealloyed Fe–3Cr–0.5Mo and 0.45 graphite. Prismatic samples of (120 mm 30 mm 15 mm) were cold pressed at 600 MPa. The samples corresponding to Mat1 and Mat2 were double-pressed and double-sintered: presintered at 800 8C for 45 min in furnace under a N2/H2 atmosphere, repressed to a density around 7.0–7.1 g/cm3 and finally sintered for 30 min in a belt furnace at 1135 8C under endogas. Mat3 samples were pressed to an average density of 6.95– 6.98 g/cm3 and sintered for 45 min in a roller furnace at 1135 8C under a 90N2–10H2 atmosphere. Finally, 50% of the samples were tempered for 45 min at 180 8C. The different specimens (tensile and SPT) were machined from the prismatic samples showed in Fig. 3a and their geometry and situation are summarized in Fig. 3b. Tensile specimens had a width of 4 mm, thickness of 0.5 mm thick and a gauge length of 25 mm. Knowing the influence of porosity on the mechanical properties of these materials, two different thickness locations were analyzed (mid-thickness and surface, m and s respectively).
FIGURE 2
FIGURE 3
The carbon content, evaluated on both surfaces of the different samples, using a standard Leco analyzer, is summarized in Table 1. This table also shows the HB2.5 hardness of all the samples measured according to DIN 30910 (Part 4) and the density results, according to ISO 2738:2000. The porosity was measured by using image analysis techniques. An optical microscope Nikon Epiphot 200 was employed. It was connected to an image analyser provided with a Buehler Entreprise Omnimet software, with a standard error of 0.1%. The porosity value was obtained as the average of the measurements of 5 images per zone with a 100 magnification. It is reasonable to think that the variability of mechanical properties typical of this kind of materials, may be due to porosity differences among the specimens. In fact, a thorough analysis of these samples has shown significant porosity differences, as it is also reflected in Table 1. In the mid-thickness region (m), porosity is always larger than in the both surface (m versus s1 and s2), as a consequence of pressure heterogeneity along the vertical direction. Table 1 gathers all these porosity values. It is highlighted that significant porosity differences among the different locations were
2 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
MPRP-580; No of Pages 6 Metal Powder Report Volume 00, Number 00 March 2016
SPECIAL FEATURE
SPECIAL FEATURE
TABLE 1
FIGURE 5
measured and this fact can explain differences on the measured mechanical properties
Tensile and small punch test: analysis of correlations Tensile specimens were tested according to DIN-EN-10002-1 in an Instron testing machine at a crosshead speed of 1 mm/min. SPT specimens had a standard geometry (10 mm 10 mm 0.5 mm) and were tested using the experimental device depicted in Fig. 1, mounted on a universal testing machine with a load cell of 5 kN. A punch diameter of 2.5 mm, a hole in the lower die with a diameter of 4 mm (provided by a 0.2 mm corner radius) and a displacement rate of 0.2 mm/min were used in all these tests. The brittle behavior of PM materials, well known through tensile tests, and mainly based on their porosity, was confirmed by the obtained SPT curves and by the type of failure characteristic of such samples (star cracking), and this fact also explains the high variability of their mechanical strengths, as it was demonstrated on previous works. Fig. 4 shows the characteristic SPT curves of a
FIGURE 4
ductile structural steel along with another one corresponding to a PM material used in a previous work. After a predominantly elastic zone and a slight plastification, the slope of the PM curve clearly decreases until final failure. In the case of sintered materials, being the load at onset of plastification (Py in Fig. 2) and the one corresponding to final failure (Pm in Fig. 2) so close, the correlations of the SPT resistant parameters (Py/t2 and Pm/t2) and the tensile ones are the same (expressions (4) and (5)). Fig. 4 also shows the typical ‘‘star failure’’ pattern obtained with PM materials in the SP tests. This pattern is characteristic of brittle materials (the typical SPT circumferential ductile failure is also shown in the same figure). Figs. 5 and 6 show, respectively, the tensile test and SPT curves obtained with the specimens extracted at mid-thickness (m) of the different samples. The parallelism of the results obtained with both type of tests is remarkably. Table 2 summarizes the average values and the standard deviation of both tensile and SPT parameters obtained with all materials and treatments at the different locations (near surface, s and midthickness, m).
FIGURE 6
3 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
MPRP-580; No of Pages 6 SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 March 2016
TABLE 2
SPECIAL FEATURE
The influence of the specimen location along the Z axis (Zs versus Zm) is worth to be highlighted. The mid-thickness specimens show in general lower strength and ductility than the specimens located near the sample surface. These facts can be explained, first due to the larger cooling rate suffered by the sample surface (microstructure with a higher strength [7]) and also because the porosity is larger in the center of the compacted and sintered samples, as it was already shown in Table 2 [8]. Figs. 7–9 show the correlations obtained between the tensile mechanical properties and the corresponding SPT parameters. The obtained regressions are quite good and, in the case of the yield and ultimate strengths, the obtained expressions are identical, due to the closeness of both points in both SPT and tensile test, as it was previously explained. Fig. 10 shows the values Py/t2 versus sys obtained in this work together with the obtained by Garcı´a et al. [9] using many different metallic materials. This figure also
FIGURE 7
FIGURE 8
FIGURE 9
4 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
MPRP-580; No of Pages 6 Metal Powder Report Volume 00, Number 00 March 2016
SPECIAL FEATURE
FIGURE 10
shows the Pm/t2 versus sut values also obtained in this work. We can appreciate that all the points can be adjusted by a linear regression with the same slope: s ys ¼ 0:343
Py t2
(4)
aut ¼ 0:343
Pm t2
(5)
Finally, Fig. 9 shows the correlation between the dm/t parameter obtained in the SPT test and the tensile elongation. Expression (6) describes this correlation Að%Þ ¼ 2:5387
dm þ 1:41 t
(6)
Verification using new synchronizer hubs In order to study the accuracy of the mentioned correlations (expressions (4), (5) and (6)) and the influence of porosity on the mechanical properties of sintered material, new tests were carried out using commercial synchronizer hubs produced with a diffusion-bonded commercial powder of nominal composition Fe–0.5Mo–1.5Cu–4.0Ni (0.5% graphite and 0.8%wax). The
FIGURE 11
samples were double-pressed and double-sintered: repressed to a density between 7.0 g/cm3 and 7.1 g/cm3 and finally sintered for 30 min in a belt furnace at 1135 8C under an endogas atmosphere (SYH1 samples). Finally, 50% of the synchronizer hubs were tempered at 180 8C for 45 min (SYH2 samples). Fig. 11 shows the geometry of the analyzed synchronized hubs. Tensile and SPT specimens were extracted from the three sectors of the hubs at the locations and orientations shown in Fig. 5 (this figure only shows the extraction made on a single sector of the component). Tensile specimens 4 mm wide, 0.5 mm thick and with a gauge length of 25 mm were tested according to DIN-EN10002-1 in an Instron testing machine at a crosshead speed of 1 mm/min. standard SPT specimens were extracted in the same positions than tensile ones. Moreover, the average porosity of the three sectors of the synchronizer hub was also metallographically measured using image analysis. Table 3 summarizes the tensile test properties obtained in the different sectors of the analyzed synchronizer hubs along with their respective porosities. The obtained results (tensile parameters and porosity) are quite homogeneous and an average porosity of 6.25% was determined. It is also worth to mention the slight improvement of the resistant properties (elastic modulus and yield and tensile strengths) after tempering. By the contrary, tempering does not seem to affect ductility. The homogeneity observed in the tensile tests was also a feature characteristic of the small punch results. Fig. 12 shows the SPT curves obtained with samples machined from the different sectors of the SYH2 (curves have been corrected using the original sample thickness). Table 4 summarizes the average values and the standard deviation of the SPT parameters obtained with samples machined from
FIGURE 12
5 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056
SPECIAL FEATURE
TABLE 3
MPRP-580; No of Pages 6 SPECIAL FEATURE
Metal Powder Report Volume 00, Number 00 March 2016
SPECIAL FEATURE FIGURE 13
TABLE 4
SPT specimens in cases where samples have a same amount of porosity. Finally, it is worth to highlight again the utility of the SPT methodology to carry out the mechanical characterization of PM products.
Conclusions
the different sectors of all the analyzed synchronizer hubs. Moreover, Table 4 shows the values of porosity obtained in the different analyzed sectors. We can see the high homogeneity of the porosity values and how this is reflected in the low dispersion of the SPT parameters. In addition, these porosity values are very similar to those obtained in the tensile specimens (Table 3). Fig. 13 shows the correspondence between the SPT resistant parameters (Py/t2, Pm/t2) and the tensile ones (sy and su) obtained in this work along with the results obtained in previous works [9]. As can be seen, the values obtained in this work lie within the typical dispersion range showed for a great number of different metallic materials. Furthermore, the fact that the correlation points obtained in this work lie above the average straight line may be related with the low porosity of the hub samples, opening the door to a better prediction of their mechanical properties using
The applicability of the small punch test to mechanically characterize powder metal products has been demonstrated and valid correlations have been proposed in order to obtain their tensile mechanical properties from the typical SPT parameters. By means of the proposed correlations, the tensile properties of sintered products manufactured using three different powders were determined and also the mechanical properties at different locations of synchronizer hubs. Moreover, the benefits of applying a tempering treatment at the final product are also worth to be remarked. References [1] [2] [3] [4] [5] [6] [7]
M. Suzuki, M. Eto, K. Fukaya, et al. J. Nucl. Mater. 179–181 (1991) 441–444. D. Finarelli, M. Roedig, F. Carsughi, J. Nucl. Mater. 328 (2004) 146–150. C. Rodrı´guez, J. Garcı´a, E. Ca´rdenas, C. Betego´n, Weld. J. 88 (2009) 188–192. X. Mao, H. Takahashi, J. Nucl. Mater. 150 (1987) 42–52. E. Fleury, J.S. Ha, Int. J. Pres. Ves. Pip. 75 (1998) 699–706. Y. Ruan, P. Spa¨tig, M. Victoria, J. Nucl. Mater. 307–311 (2002) 236–239. Influence of microstructure and porosity on fatigue properties of sintered steels, B. ¨ gana¨s AB, Ho ¨ gana¨s Sweden. Lindqvist, Ho ¨ gana¨s AB, Sweden, 1967. [8] BOCKSTIEGEL, G., Unpublished data held by Ho [9] T.E. Garcı´a, C. Rodrı´guez, F.J. Belzunce, C. Sua´rez, J. Alloys Compd. 582 (2014) 708–717.
6 Please cite this article in press as: M. Ferna´ndez, et al., Met. Powder Rep. (2016), http://dx.doi.org/10.1016/j.mprp.2016.02.056