## 1 Introduction  
Mechanical seal directly affects the thermal control and reliable operation of rotary machinery equipment, such as turbines, centrifugal compressors, communication radars, and so on. As operating conditions become more demanding, rotary seals are faced with more severe environments, such as conditions with low rotational speeds, swinging, and impacts. At low rotational speeds, an effective liquid film cannot be formed by the rotary and stationary rings of a mechanical seal, creating key issues such as friction damage and wear failure.  
The friction and wear of the end surfaces of mechanical seals have been extensively investigated. Most studies have been based on experimental and simulation analyses. [PERSON] et al. [1] designed test equipment to conduct end surface friction and wear tests on mechanical seals with tungsten carbide and resin-impregnated carbon pairs. The friction characteristics of different lubrication conditions could be analyzed by this equipment. [PERSON] et al. [2] analyzed the local vibrations of a tribological system under interfacial lubrication conditions and verified the tribological performances of carbon and tungsten carbide seal pairings under different lubrication environments by studying the complex global response caused by local interface behavior. The trends of the leakage rate changes were determined by designing a test device to control the stability of the friction coefficient and change the surface roughness of the seal rings [3, 4, 5]. [PERSON] et al. [6] conducteda test experiment on the wear resistance of mechanical seal rings for pumps. The friction and wear of rotary and stationary sealing rings is more prominent under low-rotational-speed and light-load operations. [PERSON] et al. [7] studied the theory of the surface micro-structure and confirmed that the hydrodynamic pressure effect was well controlled and improved by the surface micro-structure. The results of the study showed that the lubricating liquid and wear debris could be stored by the surface micro-structure. What's more, the performance of wear has been significantly improved by striped grooves and lattice dimples with small pitches [8]. In addition, [PERSON] et al. [9] used lasers to produce different types of grooves and found that the hydrodynamic pressure effect in the grooves generated an additional load-carrying force. To further improve the fluid carrying capacity, [PERSON] et al. [10] applied an NSGA-II algorithm to further optimize the texture shapes and discussed the effects of the texture geometric parameters on the sealing performance. The results showed that the seal opening force is increased by more than 20% by a change in texture [11; 12; 13]. Subsequently, [PERSON] et al. [14] and [PERSON] et al. [15] conducted actual tests on friction pairs with surface modifications and showed that the sealing lubricity and friction were improved by the textures of the end surfaces of the friction pairs. However, there are few studies on the friction performance of mechanical seal friction pairs under low rotating speed (\(n_{\text{r}}\leq 300\) rpm), and there is a lack of research on the composite pattern texture of micro-grooves and micro-dimples. Thus, friction pair pairing schemes and bi-composite surface texture configurations are worth studying.  
Based on the idea of texture in the rotating ring of a mechanical seal, this paper puts forward interesting patterns in which the micro-grooves and micro-dimples were combined in double rings (rotating and static rings), to which we refer as bi-composite surface texture configurations. It was designed in order to study the friction performance of a mechanical seal in low speed. This paper was mainly studied from three aspects, namely, friction pairs with different materials, single texture pattern, and bi-composite surface texture configurations in the surface of the friction pairs. Subsequently, the friction coefficients, temperatures, wears, and surface morphologies were analyzed in detail for use in the design of a mechanical seal.