Abstract
The microstructure, immersion corrosion behaviour in simulated body fluid and mechanical properties of Zn-1.2Cu-1.2Mg-xGd (x=0, 0.1, 0.25, 0.5, wt%) alloys were studied. The results show that the microstructure of zinc alloy is mainly composed of Zn solid solution and Mg2Zn11 intermetallic compound. When Gd addition content is 0.5wt%, the GdZn12 intermetallic compound appears. The microhardness of zinc alloy increases with the increase of Gd addition content, and when the addition content of Gd is 0.5wt%, the microhardness reaches maximum, 1530 MPa. The tensile strength increases first and decreases afterwards, and when the Gd addition content is 0.25wt%, the zinc alloy has high tensile strength. Zinc alloy with 0.1wt% Gd addition content has the lowest corrosion rate.
Science Press
As a new biodegradable metallic material, zinc has attracted more and more attention. Compared with magnesium and iron, zinc has the advantages of low melting point, good formability, etc. More importantly, the degradation rate of zinc in simulated body fluid is slower than that of magnesium and faster than that of iron, and more in accordance with the requirement of human body implant than other metal
As an alloying/microalloying element, rare earth metals have been found useful in the development of new biodegradable magnesium alloys or in the improvement of strength and the regulation of degradation rat
Pure Zn (99.9wt%), pure Mg (99.9wt%), pure copper (99.9wt%) and master alloy Mg-30Cd were used as raw materials, Zn-1.2Cu-1.2Mg-xGd (x=0, 0.1, 0.25, 0.5, wt%) alloys were prepared by melting in a graphite crucible with a resistance furnace and poured into a metal mold at 150 °C. The metallographic examination was carried out by Olympus GX51 metallographic microscope, and the composition (wt%) of metallographic corrosion agent was CrO3:Na2SO4:H2O=20:1.5:100.
The microstructure, corrosion surface morphology and tensile fracture surface morphology of the alloy were analyzed by JSM-6380LV scanning electron microscope (SEM) equipped with energy spectrum analyzer (EDS). The phase composition of alloy was analyzed by X-ray diffractometer (Bruker d 8advance) with Cu target, tube current 40 mA, tube voltage 40 kV, testing range from 10° to 90°, and scanning speed 10°/min. The mechanical properties were analyzed by material testing machine (Zwick/Roell Z030, Germany) at room temperature and drawing rate of 1 mm/min. Three samples were tested under the same conditions. The microhardness of alloy was measured by FM700 microhardness tester. Test conditions are as follows: pressure head load 1 N, loading time 15 s. The microhardness was tested at ten different locations of the alloy sample, and then averaged.
The corrosion behavior of zinc alloy was studied by electrochemical workstation (Parstat 2273) and simulated body fluid immersion test. In the electrochemical process, a three-electrode system was adopted, with saturated calomel electrode (KCl) as reference electrode, platinum plate as auxiliary electrode and sample as working electrode. The corrosive medium was 3.5wt% NaCl solution. The test area of the working electrode was 1 c
As shown in the metallographic photographs of Fig.1a, 1c, 1e and 1g, the microstructure of Zn-1.2Cu-1.2Mg-xGd(x=0, 0.1, 0.25, 0.5, wt%) alloys consists mainly of light-colored dendrite and dark-colored structure, the size and content of dendrite decrease with the increase of Gd addition content. The results of EDS analysis show that the Zn content is 97.94at% and Cu content is 2.06at% in the light-colored dendrite. The light-colored dendrite is Zn solid solution containing Cu, as shown in Fig.1i. The dark-colored structure contains Zn, Cu and Mg, with contents of 91.76at%, 1.64at% and 6.60at%, respectively, as shown in Fig.1.
With the addition of Gd, the microstructure labeled by “O” appears in Fig.1h containing Zn (92.29at%) and Gd (7.71at%), which is different from the area labeled by “M” and “N” in Fig.1b. The XRD pattern of Fig.1l shows that the light-colored dendrite is Zn solid solution and the dark-colored structure is intermetallic compound of Mg2Zn11. When the Gd addition content is 0.5wt%, the GdZn12 is found in the XRD pattern of zinc alloy. As shown in Fig.1b, 1d, 1f and 1h, the dark-colored structure in Fig.1a, 1c, 1e and 1g appears as a lamellar structure. It also shows that the microstructure is a eutectic structure composed of Zn and Mg2Zn11 intermetallic compound. Part of dendrites break off and a large number of fine, more evenly distributed grains appear at 0.25wt% Gd addition, as shown in Fig.1f. The dendrite is basically broken, and the fine grains show segregation with 0.5wt% Gd addition, as shown in Fig.1h. The microstructure is refined and the tendency of dendrite growth is reduced with reasonable addition content of Gd. Segregation occurs and the amount of dendrite structure increases slightly with excessive Gd addition.
Fig.2 shows the corrosion morphology and EDS analysis of corrosion products of Zn-1.2Cu-1.2Mg-xGd (x=0, 0.1, 0.25, 0.5) zinc alloys in Hank's solution. From Fig.2a~2d, the corro-sion morphology of the alloy surface is affected by the addition content of Gd in zinc alloy. Serious local corrosion occurs on the alloy surface without Gd addition, and corrosion pits appear when the local corrosion products are separated from the surface. Protruding corrosion products appear on the local surface and local corrosion occurs at 0.1wt% Gd addition content. With the increase of Gd addition content to 0.25wt%, the granular corrosion products are uniformly co-vered on the surface, showing uniform corrosion. With the increase of Gd addition content to 0.5wt%, the corrosion sur-face of the sample is smooth and full of corrosion cracks.
The EDS analysis of corrosion product shows that O, Ca and P elements are rich in the corrosion products of alloy surface with 0.25wt% Gd addition content, which are 39.83at%, 25.34at% and 24.37at%, respectively. While, the contents of O, Ca and P elements are 11.22at%, 5.86at% and 9.45at% in corrosion products with 0.5wt% Gd addition, and Ca and P are the components of Hank's solution. According to Ref.[
Fig.3 shows the polarization curve and corrosion rate of Zn-1.2Cu-1.2Mg-xGd (x=0,0.1,0.25,0.5) alloy. As can be seen from Fig.3a, the corrosion resistance of alloy is improved with Gd addition. When Gd addition amount is 0.1wt%, it shows better corrosion resistance, and the self-corrosion potential and current density are -1.221 V and 1.258 μA/c
According to surface corrosion morphology in Fig.2a~2d, the samples with 0.1wt% and 0.5wt% Gd addition amount may form a dense and adhesive corrosion product, which acts as a barrier layer and slows down the corrosion of the alloy. However, the surface corrosion products of as-cast samples with 0.25wt% Gd addition amount are loose porous, and the bonding force with the base metal is weak. In the process of immersion, the corrosion products form on the alloy surface, then fall off, exposing a new surface, and the base metal is continuously corroded. It can be seen from Fig.3b that the corrosion rates of the alloys are 0.705, 0.069, 0.128 and 0.202 mm/a with the increase of Gd addition content, which are consistent with the corrosion process of zinc alloy.
Fig.4 shows the tensile strength and hardness (Fig.4a) and stress-strain curves (Fig.4b) of Zn-1.2Cu-1.2Mg-xGd (x=0, 0.1, 0.25, 0.5, wt%) zinc alloy. From Fig.4a, the average microhardness of zinc alloy increases with increasing the addition content of Gd, from 1350 MPa (without Gd addition) to 1530 MPa (with 0.5wt% Gd addition), and the tensile strength increases at first and then decreases. When the addition content of Gd is 0.25wt%, the tensile strength and elongation of zinc alloy reach the maximum value, 228 MPa and 0.46%, respectively.
From Fig.4b, zinc alloy with 0.25wt% Gd addition amount shows better mechanical property compared with other zinc alloys. The tensile strength is very sensitive to the grain size of the alloy. According to Hall-Petch relation, , ( is yield strength, K is constant, d is grain size), the smaller the grain size, the higher the tensile strength. When Gd addition content is 0.25wt%, the grain size of zinc solid solution is obviously refined and the effect of fine grain strengthening is remarkable, while small size GdZn12 intermetallic compounds may play a role of precipitation strengthening. When Gd addition content is 0.5wt%, GdZn12 intermetallic compound with larger size is formed, which causes the matrix to be cleaved and the tensile strength and plasticity of the alloy decrease.
Fig.5 Tensile fracture morphologies of zinc alloy with different addition amount of Gd: (a) 0wt%, (b) 0.1wt%, (c) 0.25wt%, and (d) 0.5wt%
1) The microstructure of zinc alloy is mainly composed of Zn solid solution and Mg2Zn11 intermetallic compound. When Gd addition amount is 0.5wt%, the GdZn12 intermetallic compound appears.
2) The microhardness of zinc alloy increases with the increase of Gd addition amount, but the tensile strength increases at first and then decreases. When Gd addition amount is 0.25wt%, the mechanical properties of the alloy are the best, and the tensile strength and elongation are 228 MPa and 0.46%, respectively. After Gd is added, the corrosion resistance of the alloy is improved. The alloy with 0.1wt% Gd addition amount has the smallest mass loss in simulated body fluid, which is 0.069 mm/a.
References
Seitz J M, Durisin M, Goldman J et al. Advanced Healthcare Materials[J], 2015, 4: 1915 [Baidu Scholar]
Sun Y, Kong M X, Jiao X H.Transactions of Nonferrous Metals Society of China[J], 2011, 21: 252 [Baidu Scholar]
Murni N S, Dambatta M S, Yeap S K et al. Materials Science and Engineering C[J], 2015, 49: 560 [Baidu Scholar]
Tang Z B, Niu J L, Huang H et al. Journal of the Mechanical Behavior of Biomedical Materials[J], 2017, 72: 182 [Baidu Scholar]
Zou Y L, Xia Chen Z, Chen B.Material Letters[J], 2018, 218: 193 [Baidu Scholar]
Sotoudeh Bagha P, Khaleghpanah S, Sheibani S et al. Journal of Alloys and Compounds[J], 2018, 735: 1319 [Baidu Scholar]
Sikorajasinska M, Mostaed E, Mostaed A et al. Materials Science and Engineering C[J], 2017, 77: 1170 [Baidu Scholar]
Niu J L, Tang Z B, Huang H et al. Materials Science and Engineering C[J], 2016, 69: 407 [Baidu Scholar]
Lin S, Wang Q L, Yan X H et al. Material Letters[J], 2019, 234: 294 [Baidu Scholar]
Liu P, Jiang H T, Cai Z X et al. Journal of Magnesium and Alloys[J], 2016, 4: 188 [Baidu Scholar]
Chen Y A, Wang Y, Gao J J. Journal of Alloys and Compounds[J], 2018, 740: 727 [Baidu Scholar]
Geng Z W, Xiao D H, Chen L. Journal of Alloys and Compounds[J], 2016, 686: 145 [Baidu Scholar]
Wang F, Xiao W L, Liu M W et al. Vacuum[J], 2019, 159: 400 [Baidu Scholar]
Peng Q, Huang Y, Zhou L et al. Biomaterials[J], 2010, 31: 398 [Baidu Scholar]
Hort N, Huang Y, Fechner D et al. Acta Biomaterialia[J], 2010, 6: 1714 [Baidu Scholar]
Yang L, Huang Y D, Peng Q M et al.Materials Science and Engineering B[J], 2011,176: 1827 [Baidu Scholar]
Yang D H, Chen X H, Xu X Y et al. Rare Metal Materials and Engineering[J], 2020, 49(1): 1 [Baidu Scholar]
Li H F, Xie X H, Zheng Y F et al. Scientific Reports[J], 2015, 5: 10 719 [Baidu Scholar]
Li H F, Yang H T, Zheng Y F et al. Materials and Design[J], 2015, 83: 95 [Baidu Scholar]
Tong X, Zhang D C, Zhang X T et al. Acta Biomaterialia[J], 2018, 82: 197 [Baidu Scholar]
Yang M B, Guo T Z, Li H L. Materials Science and Engineering A[J], 2013, 587: 132 [Baidu Scholar]
ASTM. Standard Practice for Laboratory Immersion Corrosion Testing of Metals, Annual Book of ASTM Standards, G31-72[S]. 2004 [Baidu Scholar]
Tang Z B,Huang H, Niu J L et al. Materials and Design[J], 2017, 117: 84 [Baidu Scholar]
Liu X, Sun J, Zhou F et al. Materials and Design[J], 2016, 94: 95 [Baidu Scholar]