I. INTRODUCTION

Section:

ChooseTop of pageABSTRACTI. INTRODUCTION <<II. MATERIALS AND METHODSIII. RESULTSIV. DISCUSSIONSV. CONCLUSIONSREFERENCESMagnesium (Mg) is a low-density material, which is frequently used in different applications, such as bio, defense, space, 3C-industry, and automotive. Mg metal is of great interest in those applications due to its machinability, strength, and toughness properties. In addition, depending on the production method, Mg alloys with different properties can be achieved. While pure Mg has insufficient properties for the mentioned applications, it can be alleviated when it is alloyed with other metals such as Al, Si, Zn, Mn, and rare elements.1–71. M. M. Avedesian and H. Baker, ASM Speciality Handbook Magnesium and Magnesium Alloys (ASM International, Material Park, OH, 1999), Vol. 274.2. B. L. Mordike and T. Ebert, Mater. Sci. Eng. A 302, 37 (2001). https://doi.org/10.1016/S0921-5093(00)01351-43. M. P. Staiger, A. M. Pietak, J. Huadmai, and G. Dias, Biomaterials 27, 1728 (2006). https://doi.org/10.1016/j.biomaterials.2005.10.0034. F. Witte, J. Fischer, J. Nellesen, H.-A. Crostack, V. Kaese, A. Pisch, F. Beckmann, and H. Windhagen, Biomaterials 27, 1013 (2006). https://doi.org/10.1016/j.biomaterials.2005.07.0375. T. Motegi, Y. Tamura, and Y. Sanpei, Canadian Patent Application 2585318 (17 April 2007).6. Y. F. Zheng, X. N. Gu, and F. Witte, Mater. Sci. Eng. R Rep. 77, 1 (2014). https://doi.org/10.1016/j.mser.2014.01.0017. Q. Chen and G. A. Thouas, Mater. Sci. Eng. R Rep. 87, 1 (2015). https://doi.org/10.1016/j.mser.2014.10.001 Mg alloys with rare elements can show high strength and corrosion/wear resistance. Mg alloys containing rare earth elements (REs) such as Y, Gd, and Nd have been exploited in the field of biomaterials in recent years. In addition, the number of papers focused on the biocompatibility and biodegradability of Mg–RE alloys is continuously increasing for a couple of years.8,98. G.-L. Jia, L.-P. Wang, Y.-C. Feng, E.-J. Guo, Y.-H. Chen, and C.-L. Wang, Rare Metals 40, 2197 (2021). https://doi.org/10.1007/s12598-020-01423-39. S. Höhn, S. Virtanen, and A. R. Boccaccini, Appl. Surf. Sci. 464, 212 (2019). https://doi.org/10.1016/j.apsusc.2018.08.173The alloying process of Mg with RE enhances the wear and corrosion resistances significantly, which, in turn, rendered those alloys’ potential candidates as biomaterials.1010. J. Li, D.-T. Zhang, F. Chai, and W. Zhang, Rare Metals 39, 1267 (2020). https://doi.org/10.1007/s12598-014-0306-3 As known, the low wear rate slows down the dissolution, which, in turn, enables the control of the biodegradation rate.1111. X. N. Gu, W. R. Zhou, Y. E. Zheng, Y. Cheng, S. C. Wei, S. P. Zhong, T. F. Xi, and L. J. Chen, Acta Biomater. 6, 4605 (2010). https://doi.org/10.1016/j.actbio.2010.07.026 Thus, the hydrogen gas (H+) release rate, which occurs with the reactions of Mg ions in the body, will slow down. This chain process can obtain an acceptable biomaterial.3,12,133. M. P. Staiger, A. M. Pietak, J. Huadmai, and G. Dias, Biomaterials 27, 1728 (2006). https://doi.org/10.1016/j.biomaterials.2005.10.00312. R.-C. Zeng, X.-T. Li, S.-Q. Li, F. Zhang, and E.-H. Han, Sci. Rep. 5, 1 (2015).13. M. Esmaily, J. E. Svensson, S. Fajardo, N. Birbilis, G. S. Frankel, S. Virtanen, R. Arrabal, S. Thomas, and L. G. Johansson, Prog. Mater. Sci. 89, 92 (2017). https://doi.org/10.1016/j.pmatsci.2017.04.011 Mg and Mg alloys introduced into the body dissolve very slowly as part of a redox reaction. During this reaction, metallic Mg (Mg atoms) is oxidized and transformed into the stable Mg+2 (Ne configuration) ion. At this time, free electrons are donated to existing H+ ions.1414. A. Yamamoto and A. Kikuta, ACS Biomater. Sci. Eng. 8, 2437 (2022). https://doi.org/10.1021/acsbiomaterials.1c01429 The Mg alloys can undergo different reactions in the presence glucose, salt, and albumin in the blood and tissues. Therefore, these affect the release and corrosion rates of the Mg alloys seriously.15–1715. W. Yan, Y.-J. Lian, Z.-Y. Zhang, M.-Q. Zeng, Z.-Q. Zhang, Z.-Z. Yin, L.-Y. Cui, and R.-C. Zeng, Bioact. Mater. 5, 318 (2020). https://doi.org/10.1016/j.bioactmat.2020.02.01516. D. Persaud-Sharma and A. McGoron, Biomater. Tissue Eng. 12, 25 (2012). https://doi.org/10.4028/www.scientific.net/JBBTE.12.2517. M. Razavi and Y. Huang, Biomater. Sci. 7, 2241 (2019). https://doi.org/10.1039/C9BM00289H For this reason, the physicochemical properties of Mg alloys should be investigated in the presence of glucose and other substances in the blood.Salt and glucose are two of the main substances affecting the performance of biomaterials in the body. In addition to these, heavy molecular substances in the connective tissue fluid can interact with their biostructures. This process affects the performance and life of the biomaterial.1818. W. Wang et al., Chem. Eng. J. 425, 129949 (2021). https://doi.org/10.1016/j.cej.2021.129949 It should be noted that reactions that take place in the presence of the substances such as glucose may result in a change in the pH of the environment; thus, it is crucial to determine the change in the physicochemical properties of the implant materials.12,15,1912. R.-C. Zeng, X.-T. Li, S.-Q. Li, F. Zhang, and E.-H. Han, Sci. Rep. 5, 1 (2015).15. W. Yan, Y.-J. Lian, Z.-Y. Zhang, M.-Q. Zeng, Z.-Q. Zhang, Z.-Z. Yin, L.-Y. Cui, and R.-C. Zeng, Bioact. Mater. 5, 318 (2020). https://doi.org/10.1016/j.bioactmat.2020.02.01519. Y. Wang, L.-Y. Cui, R.-C. Zeng, S.-Q. Li, Y.-H. Zou, and E.-H. Han, Materials 10, 725 (2017). https://doi.org/10.3390/ma10070725 Gluconic acid (GA) (C6H12O7) is formed as a result of the oxidation of glucose with water or free oxygen, and GA changes the pH of the environment.12,1912. R.-C. Zeng, X.-T. Li, S.-Q. Li, F. Zhang, and E.-H. Han, Sci. Rep. 5, 1 (2015).19. Y. Wang, L.-Y. Cui, R.-C. Zeng, S.-Q. Li, Y.-H. Zou, and E.-H. Han, Materials 10, 725 (2017). https://doi.org/10.3390/ma10070725 There may be thermodynamic obstacles in the formation of GA. During the formation, the acidic structure is reached after the reaction of glucono-lactone. Apart from GA, the formation of acetic acid (CH3COOH) and formic acid (CH2O2) can also be expected in this process. In this case, a catalyst structure may be needed.2020. S. Ramachandran, P. Fontanille, A. Pandey, and C. Larroche, Food Technol. Biotechnol. 44, 185–195 (2006). At this stage, it has been mentioned in the literature that MgO acts as a catalyst. Thus, the probability of GA formation increases or can be accelerated in Mg-containing environments.2121. N. M. Julkapli and S. Bagheri, Rev. Inorg. Chem. 36, 1 (2016). https://doi.org/10.1515/revic-2015-0010 Furthermore, the ions that emerge with the dissolution of salt in water affect the pH by acting as anions and cations.6,9,22,236. Y. F. Zheng, X. N. Gu, and F. Witte, Mater. Sci. Eng. R Rep. 77, 1 (2014). https://doi.org/10.1016/j.mser.2014.01.0019. S. Höhn, S. Virtanen, and A. R. Boccaccini, Appl. Surf. Sci. 464, 212 (2019). https://doi.org/10.1016/j.apsusc.2018.08.17322. H. Takeda, K. Nakano, N. Tanibata, and M. Nakayama, Sci. Technol. Adv. Mater. 21, 131 (2020). https://doi.org/10.1080/14686996.2020.173023723. H. Nady, M. M. El-Rabiei, A. Bahrawy, and E. E. El-Katori, J. Mol. Liq. 339, 116823 (2021). https://doi.org/10.1016/j.molliq.2021.116823 For this reason, it will be an important process to control and analyze an alloy in its interaction with these substances once it is intended as a biomaterial for use as an invasive medical device.Due to their biodegradable nature, the Mg–RE alloys give better results in temporary implant applications than those fabricated using stainless steel and titanium. Studies of Mg–RE alloy cardiovascular stents and bone scaffold structures are frequently encountered. In addition, the role of Mg as an enzyme catalyst makes this metal indispensable in the body. However, Mg+2 ions play an important role in normal mammalian physiology and in maintaining homeostasis in many tissues.2424. A. M. P. Romani, Arch. Biochem. Biophys. 512, 1 (2011). https://doi.org/10.1016/j.abb.2011.05.010 According to current knowledge, it acts not as an enzyme catalyst itself but as a mediator of many enzymes (or enzymatic catalysts).2525. J. Riordan, Ann. Clin. Lab Sci. 7, 119–129 (1977). Also, adenosine triphosphate (ATP) cannot act in the body without the ionic binding of Mg+2 ions.2626. K. Soetan, C. Olaiya, and O. Oyewole, Afr. J. Food Sci. 4, 200–222 (2010). Thus, Mg–RE alloys can be used as the basic submaterial in a stent.6,11,276. Y. F. Zheng, X. N. Gu, and F. Witte, Mater. Sci. Eng. R Rep. 77, 1 (2014). https://doi.org/10.1016/j.mser.2014.01.00111. X. N. Gu, W. R. Zhou, Y. E. Zheng, Y. Cheng, S. C. Wei, S. P. Zhong, T. F. Xi, and L. J. Chen, Acta Biomater. 6, 4605 (2010). https://doi.org/10.1016/j.actbio.2010.07.02627. S. Mischler, S. Debaud, and D. Landolt, J. Electrochem. Soc. 145, 750 (1998). https://doi.org/10.1149/1.1838341Simulated body fluid (SBF) is implemented in in vitro experiments for all biomaterials (metal, polymer, composite, etc.). SBF liquids are classified into two different classes depending on the recipe used to prepare the SBF solutions: SBF containing anion or cation ions (sometimes containing small organic molecules). Solutions, such as SBF, saliva, buffer fluid, physiological nutrient fluids, and isotonic saline, are the most commonly used types in the biomaterial experiments.28–3128. J.-C. Gao, W. Sha, L.-Y. Qiao, and W. Yong, Trans. Nonferrous Met. Soc. China 18, 588 (2008). https://doi.org/10.1016/S1003-6326(08)60102-829. H. Jia, X. Feng, and Y. Yang, Mater. Sci. Eng. C 106, 110013 (2020). https://doi.org/10.1016/j.msec.2019.11001330. A. Comba, B. Cicek, B. Comba, T. Sancak, G. A. Akveran, Y. Sun, L. Elen, and M. T. Afshar, Mater. Technol. 37, 2819 (2022). https://doi.org/10.1080/10667857.2022.208111531. M. R. C. Marques, R. Loebenberg, and M. Almukainzi, Dissolution Technol. 18, 15 (2011). https://doi.org/10.14227/DT180311P15 The dissolution mechanism and the formation of kinetics ions change depending on the composition and the type of Mg alloy. Additionally, the passivation and the rate of ions formation change depending on the environment’s pH balance. Therefore, it may be stated that the dissolution conditions in those liquids in the corrosion environment can give severe results to the biomaterial.6,7,196. Y. F. Zheng, X. N. Gu, and F. Witte, Mater. Sci. Eng. R Rep. 77, 1 (2014). https://doi.org/10.1016/j.mser.2014.01.0017. Q. Chen and G. A. Thouas, Mater. Sci. Eng. R Rep. 87, 1 (2015). https://doi.org/10.1016/j.mser.2014.10.00119. Y. Wang, L.-Y. Cui, R.-C. Zeng, S.-Q. Li, Y.-H. Zou, and E.-H. Han, Materials 10, 725 (2017). https://doi.org/10.3390/ma10070725 The modified SBF and Hanks’s solutions are frequently used in biomaterial studies. The addition of salts to SBF and Hanks’s solutions results in an evolution of more aggressive environments against biomaterials.3232. D. Tie, F. Feyerabend, N. Hort, R. Willumeit, and D. Hoeche, Adv. Eng. Mater. 12, B699 (2010). https://doi.org/10.1002/adem.201080070 Besides salts, the presence of glucose and fructose also changes the biomaterial performance in service conditions.3333. M. Zhang, C. Liao, C. H. Mak, P. You, C. L. Mak, and F. Yan, Sci. Rep. 5, 1–6 (2015). In addition, the anion and cation balances can be changed with serum albumin, blood, urea, high-Mg+2, and high-Na+ additives.22,32,34–3722. H. Takeda, K. Nakano, N. Tanibata, and M. Nakayama, Sci. Technol. Adv. Mater. 21, 131 (2020). https://doi.org/10.1080/14686996.2020.173023732. D. Tie, F. Feyerabend, N. Hort, R. Willumeit, and D. Hoeche, Adv. Eng. Mater. 12, B699 (2010). https://doi.org/10.1002/adem.20108007034. M. Maciążek-Jurczyk, A. Szkudlarek, M. Chudzik, J. Pożycka, and A. Sułkowska, Spectrochim Acta Part A 188, 675 (2018). https://doi.org/10.1016/j.saa.2017.05.02335. M. Uchida, H. M. Kim, T. Kokubo, F. Miyaji, and T. Nakamura, J. Am. Ceram. Soc. 84, 2041 (2001). https://doi.org/10.1111/j.1151-2916.2001.tb00955.x36. H. M. Liebich, G. Xu, C. Di Stefano, R. Lehmann, H. U. Häring, P. Lu, and Y. Zhang, Chromatographia 45, 396 (1997). https://doi.org/10.1007/BF0250559137. Z. Orshesh, S. Borhan, and H. Kafashan, J. Biomater. Sci. Polym. Ed. 31, 93 (2020). https://doi.org/10.1080/09205063.2019.1675226 Thus, some interpretations of the reaction of the added product in the human body can be obtained.

In this study, the WE43 alloy was prepared using the powder metallurgy method and subsequent sintering treatment. After the sintering, essential examinations were made of the sample’s microstructure, chemical composition, and hardness. In addition, a reciprocating wear test was applied to the WE43 alloys in dry and corrosive environments. Hanks’s solution (HS) and glucose-added HS (HSG) solution were used as corrosive solution. It was observed that the pH value of the solution decreased with the formation of GA, produced from the oxidation of glucose. Thus, the wear resistance of the sample in the glucose-added solution is the highest in corrosive wear. Our results indicated the potential use of WE43 alloys in body parts that come into contact with simulated body fluids.

II. MATERIALS AND METHODS

Section:

ChooseTop of pageABSTRACTI. INTRODUCTIONII. MATERIALS AND METHODS <<III. RESULTSIV. DISCUSSIONSV. CONCLUSIONSREFERENCES

In this study, WE43 powder was purchased from Nanografi Co. located in Türkiye. According to the catalog information provided by the company, this powder does not contain any other product (99.9% WE43) and the D90 value is at the level of 18 μm. WE43 powder was analyzed with a scanning electron microscope (SEM) (Carl Zeiss Ultra Plus) before use. The EDS analysis (Gemini FESEM) module coupled to the Zeiss brand SEM system was implemented for microstructural analysis. In addition, an x-ray fluorescence (XRF) (Rigaku ZSX Primus II) device was used to determine the chemical composition of the samples.

The SEM-EDS results obtained from the commercial WE43 powders are given in Fig. 1, and the chemical composition determined by the XRF method is listed in Table I.

TABLE I. XRF analysis of WE43 powders (%wt.).

AlloyAlSiCaMnNiZnYZrNdGdMgWE430.040.150.550.030.090.193.770.082.081.11balanceWE43 powders were pressed in a mini mold made of 1.0718 quality steel. This mold was purchased from Güvenal Kalıp company in Türkiye with the product number “G16316036.” The inner surface in contact with the powder has a surface quality of Ra0.8. The powder compacting punch was purchased from the same company with the product number “SBZAPM216071.” The surface quality of the press punch is reported as Ra0.5. Approximately 2 g of WE43 powder was weighed into the mold, and then, a pressing force of 20 N/mm2 was applied to form the specimens uniformly. A manual hydraulic press was used as a press with a stroke length of 50 mm. A schematic representation of the molding process is illustrated in Fig. 2.

After pressing, the samples were sintered at 450 °C for 6h by wrapping them in aluminum foil. The samples were sintered in a Protherm brand oven. A value of 100 °C/h was used as the heating rate. After 6 h, the oven was switched off and the samples were allowed to cool freely to room temperature. The cooling time was approximately 12 h.

The sintered samples were cut into approximately 2 mm plates using a precision cutting device, and the samples were molded using a hot Bakelite (about 90 °C) device. The surface of the samples was then prepared for metallographic examinations using wet sandpaper up to 2500 mesh (grain size). The polishing of the sample surface was carried out using a methanol solution containing alumina powders with a particle size of 1 μm (grain size). Finally, it was washed in methanol (high purity) and took its final form. For the metallographic examinations, no etching process was applied. After metallographic processes, the sintered samples were examined by taking SEM images at different magnifications (2k×, 5k×, and 15k×). The microstructure was subjected to EDS analysis from multiple points. X-ray diffraction (XRD) analysis was also applied to the sintered samples. Cu-based Rigaku Ultima XRD (10–90°, 2° /min) test device was used to detect phases in produced alloys. Afterward, the sintered and 2 mm thick samples were broken by a hammer blow. Thus, fracture surface images were taken to follow the details of the powder metallurgy production method (point arc, neck, joint, etc.). Finally, the primary examination is completed with volumetric and point hardness measurements (five independent measurements per sample). The hardness of the samples was measured using a micro Vickers (Qness Q10 A+) device under 1000 g (for volumetric or specimen hardness) and 10 g loads (for grain and grain boundary).

The abrasion was performed with a reciprocating motion using an AISI 420 grade ball pushed onto the moving specimen under a fixed arm and a load of 1019.72 g (10 N) (F). Each step applied a total of 100-m sliding distance (sd) at 10 mm displacement movement. Wear tests are illustrated in Fig. 3.The abrasion test was applied in two different environments: dry and corrosive environments. The composition of Hanks’s solution is given in Table II.3838. H. Kuwahara, Y. Al-Abdullat, M. Ohta, S. Tsutsumi, K. Ikeuchi, N. Mazaki, and T. Aizawa, Mater. Sci. Forum 350–351, 349 (2000). https://doi.org/10.4028/www.scientific.net/MSF.350-351.349

TABLE II. Chemicals and proportions in Hanks’s solution.

ChemicalsHanks solution (HS) (g/l)Hanks solution + glucose (HSG) (g/l)NaCl88KCl0.40.4Na2HPO4 + 2H2O0.060.06KH2PO40.060.06MgSO4 + 7H2O0.20.2CaCl20.140.14NaHCO30.350.35Glucose—2Distilled waterBalanceBalanceAfter the wear test, SEM images were taken from the worn surfaces. In addition, trace depths and types were scanned (the depth of abrasion) with the help of a profilometer (Mitutoyo SJ-410). The total eroded surface volume (WSV) was calculated with the help of the trace depth area (ta) and the amount of reciprocating movement (RMA). “Wear rate” (WR) (mm3/Nm) was calculated by applying other variables based on the equation given as follows:3939. Z. Xie, F. Guo, X. Huang, K. Li, Q. Chen, Y. Chen, and F. Gong, Vacuum 172, 109049 (2020). https://doi.org/10.1016/j.vacuum.2019.109049 WSV(mm3)=ta(mm2)×RMA(mm),(1) WR(mm3/Nm)=WSV(mm3)F(N)×sd(m),(2)where WSV is the worn surface volume, ta is the trace area, RMA is the reciprocating motion amount, WR is the wear rate, F is the load, and sd is the sliding distance.

III. RESULTS

Section:

ChooseTop of pageABSTRACTI. INTRODUCTIONII. MATERIALS AND METHODSIII. RESULTS <<IV. DISCUSSIONSV. CONCLUSIONSREFERENCESThe SEM images of pristine WE43 powder show the homogeneous particle size distribution [Fig. 1]. The presence of Mg, Y, Gd, and Nb elements with no external oxide phases and residues is confirmed by the EDS analysis. The microstructure of the sintered WE43 is displayed in Fig. 4.Even at the low magnification of the SEM overview image of the high-temperature sintered WE43 sample, the grain boundaries are clearly visible. At medium magnification, the state of the powder grains in the microstructure can be followed and a certain porosity can be observed. By using high magnification, the phase distribution in the powder grains of the WE43 alloy presented here can be seen well. It should also be mentioned here that the porosities, which are shown enlarged in Fig. 4(d) as an example, can be seen to a small extent in all SEM images. The degree of porosity in the high-temperature sintered WE43 presented here is rather low.Images taken from the sintered WE43 sample at high magnifications were examined by EDS analysis. EDS analyses from grain, grain boundary, and phase structures are shown in Fig. 5.When Fig. 5 was examined, 4.22 wt. % oxygen was detected at the grain boundary. However, this ratio has decreased below 1 wt. % on grain areas (Zone-1 0.85 wt. % and Zone-3 0.15 wt. %). EDS analyses were taken from the white phases seen in the grains. Since the elements were identified, it was known that Mg–Y (diagonal Mg24Y5 is the phase most likely to occur in Mg-rich alloys4040. A. R. Mirak, C. J. Davidson, and J. A. Taylor, J. Magn. Alloys 3, 173 (2015). https://doi.org/10.1016/j.jma.2015.06.003) and Mg–Nd phases (the phase where Nd is likely to occur up to 10% by weight is Mg41Nd54141. H. Okamoto, J. Phase Equilib. Diffus. 28, 405 (2007). https://doi.org/10.1007/s11669-007-9117-7) were likely to occur between these two elements (high magnification details taken from a clearly tracked powder). In addition, the Mg–Y phase diagram contains three intermetallic compounds. Phases called MgY, Mg2Y, and Mg24Y5 can be formed. These structures crystallize with a similar variant of the α-Mg type cubic structure.4242. M. Pekguleryuz and K. Kainer, “Alloying behavior of magnesium and alloy design,” in Fundamentals of Magnesium Alloy Metallurgy (Woodhead, Cambridge, 2013), pp. 152–196.The XRD diffractogram of the sintered WE43 is given in Fig. 6. In addition, the phases determined according to the catalog number (JCPDS numbers) are shown.According to the XRD peaks, all phases likely to be found in the WE43 alloy were found. XRD signals or peaks marked with a black filled square in Fig. 6 are α-Mg characteristic (JCPDS card No. 35-08214343. Y. Wang, Z. Gu, Y. Xin, N. Yuan, and J. Ding, Colloids Surf. A 538, 500 (2018). https://doi.org/10.1016/j.colsurfa.2017.11.055). XRD peaks or peaks marked with a black filled triangle correspond to the Y2O3 phase (JCPDS card No. 72-09274444. S.-M. Yong, D. Choi, K. Lee, S.-Y. Ko, and D.-I. Cheong, Arch. Metall. Mater. 63, 1481 (2018).). XRD peaks marked with a black circle indicate the Mg24Y5 phase (JCPDS card No. 31-08174545. Q.-Q. Jin, C.-F. Fang, and S.-B. Mi, J. Alloys Compd. 568, 21 (2013). https://doi.org/10.1016/j.jallcom.2013.03.061). XRD peaks marked with black diamond belong to the Mg41Nd5 phase (JCPDS card No. 00-045-103146,4746. L. Elen, Y. Turen, H. Ahlatci, M. Unal, and D. Ergin, Biointerphases 17, 041001 (2022). https://doi.org/10.1116/6.000185847. E. Levent, Düzce Üniversitesi Bilim ve Teknoloji Dergisi. 10, 1372 (2022).). Phases and peak intensities show the same characteristics as in the literature.48–5048. A. Inoue, Y. Kawamura, M. Matsushita, K. Hayashi, and J. Koike, J. Mater. Res. 16, 1894 (2001). https://doi.org/10.1557/JMR.2001.026049. P.-W. Chu and E. A. Marquis, Corros. Sci. 101, 94 (2015). https://doi.org/10.1016/j.corsci.2015.09.00550. S. Gangireddy, B. Gwalani, K. Liu, E. J. Faierson, and R. S. Mishra, Addit. Manufact. 26, 53 (2019). https://doi.org/10.1016/j.addma.2018.12.015To complete the analysis of the polished surfaces of the high-temperature sintered Mg alloy WE43 using SEM, EDS, and XRD, a typical fracture surface SEM overview and a cross-sectional magnification are shown in Fig. 7.SEM image should be examined under two headings. First, the amount of load (20 N/mm2) applied during molding did not change the spherical form of the powder grains. No fragmentation or breakage occurred in the powder grains. Adhesions were formed between the powder grains by a bonding with mechanical force. Thus, the molded sample was not deformed during sintering. Second, when the fracture surface images were examined, it was observed that the expected “neck” and “joint” structures were formed in the powder metallurgy samples. The “neck” mechanism can be called the step of connecting the powder grains from the contact surfaces to each other. The “joint” mechanism is the beginning of a grain boundary formed between powders.51,5251. B. Cicek, Y. Sun, Y. Turen, and H. Ahlatci, Sci. Sinter. 54, 25 (2022). https://doi.org/10.2298/SOS2201025C52. H. He, J. Lou, Y. Li, H. Zhang, S. Yuan, Y. Zhang, and X. Wei, Powder Technol. 329, 12 (2018). https://doi.org/10.1016/j.powtec.2018.01.036Hardness measurements taken from the produced WE43 alloy are given in Fig. 8. Volumetric hardness, grain boundary hardness, and grain hardness are important processes in the powder metallurgy product after sintering. In addition to the hardness measurements, the stinging tip trace images are included in Fig. 8.

According to the hardness test results, the sample’s average hardness was found to be 53 HV in volumetric measurement. While the hardness was 65 HV at the grain boundary, it reached 71 HV in the grain.

Finally, the results obtained in the abrasion test applied to the WE43 sample are shown in Fig. 9.

When the worn surface images were examined, it was observed that abrasive structures were formed in dry wear. In dry wear (a), microcracks were formed at the grain boundaries. In the corrosive wear (b) in HS, fragment rupture occurred with corrosion progression at the grain boundaries. In HSG corrosive wear, (c) the layers formed on the grain surfaces formed an adhesive structure on the wear surface.

When the amount of worn surface trace area was examined, it was measured as 0.413 mm2 in dry wear. In HS and HSG, 0.558 and 0.349 mm2 eroded field depth measurements were determined, respectively.

WR was calculated over the trace depth field values measured after the wear test [formulas (1) and (2)]. According to these results, the graph of wear rates is given in Fig. 10.

According to the WR levels obtained after the test, the least volume loss occurred in the experiment performed in HSG. In the experiment performed in HS, the highest wear rate was measured.

IV. DISCUSSIONS

Section:

ChooseTop of pageABSTRACTI. INTRODUCTIONII. MATERIALS AND METHODSIII. RESULTSIV. DISCUSSIONS <<V. CONCLUSIONSREFERENCESThe SEM and EDS results of the commercial WE43 powders indicated the presence of the RE elements that are expected to be found in WE43 powders reported in the literature (Fig. 1).39,49,5339. Z. Xie, F. Guo, X. Huang, K. Li, Q. Chen, Y. Chen, and F. Gong, Vacuum 172, 109049 (2020). https://doi.org/10.1016/j.vacuum.2019.10904949. P.-W. Chu and E. A. Marquis, Corros. Sci. 101, 94 (2015). https://doi.org/10.1016/j.corsci.2015.09.00553. T. Rzychoń and A. Kiełbus, J. Achiev. Mater. Manufact. Eng. 21, 31 (2007).As a result of powder metallurgy production and fundamental microstructure analysis of the WE43 alloy [Figs. 4 and 5], the results were compatible with the literature. In powder metallurgy products, some mechanisms must be formed as a result of sintering.51,52,5451. B. Cicek, Y. Sun, Y. Turen, and H. Ahlatci, Sci. Sinter. 54, 25 (2022). https://doi.org/10.2298/SOS2201025C52. H. He, J. Lou, Y. Li, H. Zhang, S. Yuan, Y. Zhang, and X. Wei, Powder Technol. 329, 12 (2018). https://doi.org/10.1016/j.powtec.2018.01.03654. R. M. German, Powder Metallurgy Science (Metal Powder Industries Federation, Princeton, NJ, 1984). “Neck” mechanism and “joint” mechanism are observed in the microstructures [Fig. 4] and fractured surface [Fig. 6]. In addition, porosity did not occur at the grain boundaries where the two powder grains met. Low porosity was observed at the corner points where three more grains coincided (Fig. 4).Pure Mg element has high oxygen affinity.5555. F. Czerwinski, Corros. Sci. 86, 1 (2014). https://doi.org/10.1016/j.corsci.2014.04.047 However, the WE43 Mg alloy was used in this study. The oxygen affinity of Mg alloys shows a serious decrease compared to their pure form.5656. F. Czerwinski, J. Mater. 64, 1477 (2012). https://doi.org/10.1007/s11837-012-0477-z The free oxygen that can accumulate on the powder surfaces used in the powder metallurgy method during mixing and preparation should be limited.5757. J. Liao, M. Hotta, and A. Koshi, Mater. Lett. 65, 2995 (2011). https://doi.org/10.1016/j.matlet.2011.06.028 These oxygen residues cause oxidation during sintering. Since the oxidation process of the Mg metal is very fast and violent, the structure must be free of oxygen.22,5822. H. Takeda, K. Nakano, N. Tanibata, and M. Nakayama, Sci. Technol. Adv. Mater. 21, 131 (2020). https://doi.org/10.1080/14686996.2020.173023758. K. R. Anderson, J. R. Groza, M. Fendorf, and C. J. Echer, Mater. Sci. Eng. A 270, 278 (1999). https://doi.org/10.1016/S0921-5093(99)00197-5 However, it should be noted that the amount of free oxygen is present in powder metallurgy although it is concentration is low.59,6059. M. Wolff, T. Ebel, and M. Dahms, Adv. Eng. Mater. 12, 829 (2010). https://doi.org/10.1002/adem.20100003860. R. German, Sintering from Empirical Observations to Scientific Principles (Elsevier, New York, 2014). The EDS analysis (Fig. 5) showed that oxide was only found at the grain boundaries. This level is at most 4% of the total microstructure (grain boundary). The oxygen ratio in grains remained below 1 wt. %. This oxide level does not affect the general structure at the microscopic level.Mg24Y5 phase between Mg and Y in the WE43 alloy was detected in both EDS analysis [Fig. 5] and XRD spectrum [Fig. 6]. This phase, which is harder than the Mg element, has been observed on powder surfaces.4848. A. Inoue, Y. Kawamura, M. Matsushita, K. Hayashi, and J. Koike, J. Mater. Res. 16, 1894 (2001). https://doi.org/10.1557/JMR.2001.0260 In addition, the Mg24Y5 phase, which shows a diagonal form similar to the literature, was determined.5050. S. Gangireddy, B. Gwalani, K. Liu, E. J. Faierson, and R. S. Mishra, Addit. Manufact. 26, 53 (2019). https://doi.org/10.1016/j.addma.2018.12.015 In terms of type and analysis, it was similar to the studies by Inoue et al.4848. A. Inoue, Y. Kawamura, M. Matsushita, K. Hayashi, and J. Koike, J. Mater. Res. 16, 1894 (2001). https://doi.org/10.1557/JMR.2001.0260 and Chu et al.4949. P.-W. Chu and E. A. Marquis, Corros. Sci. 101, 94 (2015). https://doi.org/10.1016/j.corsci.2015.09.005 The Mg41Nd5 phase formed between Mg and Nd in the WE43 alloy was detected in XRD analysis. In Fig. 5, this phase was detected in the structures on the grains. The geometric phase type gave similar results to the literature.5353. T. Rzychoń and A. Kiełbus, J. Achiev. Mater. Manufact. Eng. 21, 31 (2007).Different phases were detected in WE43, an Mg–RE alloy, according to XRD analysis [Fig. 6]. The sintering temperature was determined based on the formation temperature of the phases in the Mg–Y binary phase diagram. For the Mg24Y5 phase, at least 2.16% Y is required. This phase can also occur in the range of about 200–550 °C.61,6261. D. Mizer and J. Clark, Trans. Met. Soc. AIME 221, 207 (1961).62. Y. Guo, J. Li, J. Li, Z. Yang, J. Zhao, F. Xia, and M. Liang, J. Alloys Compd. 450, 446 (2008). https://doi.org/10.1016/j.jallcom.2006.10.125 Likewise, the Mg–Nd binary phase diagram is also taken into account at this stage.41,6241. H. Okamoto, J. Phase Equilib. Diffus. 28, 405 (2007). https://doi.org/10.1007/s11669-007-9117-762. Y. Guo, J. Li, J. Li, Z. Yang, J. Zhao, F. Xia, and M. Liang, J. Alloys Compd. 450, 446 (2008). https://doi.org/10.1016/j.jallcom.2006.10.125 The Mg41Nd5 phase, which is expected between Mg and Nd, can occur in the structure up to a temperature level of 548 °C.4141. H. Okamoto, J. Phase Equilib. Diffus. 28, 405 (2007). https://doi.org/10.1007/s11669-007-9117-7 Thus, the expected phase struct