Yan Shuaijiang 1, Li Aiguo 1, Nie Mengjie 1, Guan Keke 1, 2, Li Xin 1, Long Weimin 1
(1. State Key Laboratory of High Performance & Advanced Welding Materials, China Academy of Machinery Zhengzhou Research Institute of Mechanical Engineering Co., Ltd., Zhengzhou 450001, Henan, China; 2. School of Mechanical Engineering, Henan University of Engineering, Zhengzhou 451191, Henan, China)
Extended abstract:
[Background and purposes] High-performance grinding wheels play a critical role in determining workpiece quality and machining efficiency. The properties of grinding wheels are largely determined by the bond composition. Vitrified bonds are widely used in the fabrication of high-precision grinding wheels, due to their advantages of high hardness, wear resistance, thermal stability and chemical stability. However, the interaction mechanisms among the components of vitrified bonds are not fully revealed, hindering further performance improvement and application expansion. This study was aimed to study on the effects of compositions on the microstructure and properties of SiO2-Al2O3-B2O3-R2O based vitrified bonds. The objective is to reduce the preparation temperature of the vitrified bonds, with simultaneous enhancement of mechanical strength through optimized compositional design, thereby providing reliable bond material for the fabrication of high-performance grinding wheels.
[Methods] SiO2-Al2O3-B2O3-R2O based vitrified bond was prepared by using high-temperature melting and water quenching method. SiO2, Al2O3, B2O3, Li2O and Na2O powders, with various compositions, were uniformly mixed with ball milling. Then, the mixtures were melted at 1400 ℃ for 0.5 h and immediately water-quenched to room temperature. The obtained vitrified bond was crushed and passed through 200-mesh sieve. The vitrified bond powders were compressed into the dimension of 35 mm 5 mm5 mm using a steel mold. The samples were then sintered at 570–900 ℃ for 2 h. Phase composition of the vitrified bond was examined by using X-ray diffraction (XRD) with Cu Kα radiation, over 2θ range of 10°–80°, at a step size of 0.02°. Microstructure and elemental distributions of the vitrified bond material were characterized by using scanning electron microscopy (SEM). Hardness measurements were performed using a Vickers hardness tester under a load of 4.9 N with a dwelling time of 30 s. Strength of the samples was tested using the three-point bending method, with a span length of 20 mm and a crosshead speed of 0.5 mm·min−1. Additionally, wear resistance of the grinding wheel specimens was evaluated through abrasive wear tests.
[Results] The XRD results indicate that the four vitrified bonds primarily contain amorphous phase, suggesting that the preparation method used in this work is suitable for vitrified bonds. SEM characterization results reveal that the microstructure of the bond samples is homogeneous and numerous closed pores with different sizes are distributed throughout the matrix. The pores in the A-3 sample are uniformly distributed, while the A-2 sample contains the minimum number of pores. The elemental distribution map shows that the major elements of Si, Al, Na, and O are uniformly distributed within the vitrified bond matrix with no significant agglomeration. The A-2 vitrified bond possesses the lowest refractoriness of 720 ℃, due to the highest B2O3 content in this sample. The refractoriness of A-1 increased to 740 ℃ with a lower B₂O₃ content than A-2 sample. The A-4 vitrified bond contains a relatively high proportion of high-melting phase Al2O3, thus exhibiting a higher refractoriness of 860 ℃. In the A-3 bond, the Al2O3 content is further increased, leading to a refractoriness of up to 900 ℃. However, the fluidity of the vitrified bonds shows an opposite trend to the refractoriness. The A-3 binder achieves a maximum hardness of 5.9 GPa after sintering at 840 ℃ for 2 h. The hardness of the A-1 and A-4 bonds decreases to 4.6 GPa and 4.5 GPa, respectively. The A-2 sample reaches its minimum hardness of 4.3 GPa after sintering at 660 ℃ for 2 h. The three-point bending test results indicate that the strength of the four bonds tends to increase initially and then decrease with the increasing of sintering temperature. After sintering at 840 ℃ for 2 h, the A-3 binder attains the maximum flexural strength of 134.4 MPa, which is considerably higher than the strength reported in the open literature. This is due to the A-3 bond having the highest Al2O3 content along with moderate Li2O and Na2O levels. Therefore, Al2O3 can acquire additional free oxygen to form [AlO4] tetrahedra, which provides a significant strengthening effect. After the abrasive wear test, the surface roughness of the grinding wheel sample increases, which is mainly attributed to the detachment of the vitrified bond.
[Conclusions] The contents of Al2O3 and B2O3 directly influence the strength of SiO2-Al2O3-B2O3-R2O vitrified bonds. When the contents of Al2O3 and B2O3 are 20 wt.% and 10 wt.%, respectively, the sample exhibits a maximum flexural strength of 134.4 MPa, which is higher than the strengths reported in the literature. A higher B2O3 content in the vitrified bond leads to a lower refractoriness. Furthermore, the fluidity of the bonds exhibits an opposite trend to refractoriness. The ceramic bond in this work can uniformly connect the SG abrasives. During the grinding process of the fabricated abrasive tool samples, the vitrified bonds were preferentially worn and then the abrasives gradually become rounded with the increasing of sample surface roughness. This result can be used as an important reference for the compositional design and application of low-temperature high-strength vitrified bonds.
Key words: vitrified bond; microstructure; mechanical properties; corundum grinding wheel; abrasive wear