In this research, a new metal matrix nanocomposite with enhanced capability for biomedical applications was fabricated by incorporation of nano-sized hydroxyapatite (HA) particles within the titanium substrate using multi-pass friction-stir processing (FSP). These n-HA particles were dispersed effectively within the titanium matrix. Titanium metal-matrix was processed without introducing the HA nanoparticles, as well, for the aim of comparison. The results showed the formation of different regions with various microstructural features and mechanical property across the processed materials. A thin layer with ultra-fine grain structure and indentation hardness value of up to ~400 HV was formed on the surface after FSP modification of coarse-grained titanium substrate. This was due to severe shear deformation induced by the rotating shoulder as well as the surface absorption of N and O elements from the atmosphere inside the layer. Incorporation of nanoparticles and subsequent grain structural refinement owing to operative dynamic recrystallization mechanisms leads to a maximum hardness improvement of up to ~250 HV in the lower regions (as compared to the average hardness value of base metal ~150 HV). The FSP modified pure titanium exhibited a good combination of strength and ductility by refining the grain structure with a well-developed dimple-like structure on the fracture surface. For the nanocomposite specimen, the trend of the tensile property was found deteriorative showing the impaired features on the fracture surface. This is attributed to the complex structure of HA compound and low quality of interfacial bonding between the nanoparticles and titanium matrix.

在这项研究中，通过使用多道次搅拌摩擦处理（FSP）将纳米级羟基磷灰石（HA）颗粒掺入钛基材中，制造出一种具有增强的生物医学应用能力的新型金属基纳米复合材料。这些n-HA颗粒有效地分散在钛基质中。出于比较的目的，钛金属基体也未引入HA纳米粒子进行处理。结果表明在整个加工材料中形成了具有各种微结构特征和机械性能的不同区域。在对粗晶粒钛基体进行FSP改性之后，在表面上形成了具有超细晶粒结构和压痕硬度值高达〜400 HV的薄层。这是由于旋转肩部引起的严重剪切变形，以及层内大气中N和O元素的表面吸收所致。由于有效的动态再结晶机制，纳米颗粒的掺入和随后的晶粒结构细化导致下部区域的最大硬度提高到〜250 HV（与贱金属的平均硬度值〜150 HV相比）。FSP改性的纯钛通过在断裂表面上细化具有良好发展的凹坑状结构的晶粒结构，表现出强度和延展性的良好组合。对于纳米复合材料样品，发现拉伸性能的趋势恶化，显示出断裂表面上的特征受损。