After any new medical titanium alloy material is designed and established, only easy to be processed into plates, tubes, rods, strips and other conventional materials of different shapes and specifications can meet the needs of subsequent precision machining of different surgical implant products. Titanium alloy plates, titanium alloy rods, titanium alloy tubes, titanium alloy forgings and other semi-finished billets first need to use high temperature (usually above the alloy phase transition point) large plastic deformation to fully break the original coarse as-cast structure, and the commonly used hot pressure processing equipment or methods mainly include free forging, precision forging, rapid forging, etc. The raw materials used for precision machining of titanium alloy surgical implants and orthopedic instruments commonly used in the market are mainly small-size plate, tube, rod, thread, silk, foil and other deep-processed products, which can be obtained by four processing methods, such as extrusion, rolling, rotary forging and drawing.
Compared with coarse-grained materials, ultrafine crystalline materials with micro - and nano-structures (typical sizes in their crystal regions or other characteristic lengths reach 100 nm~1 in at least one dimension direction) are found μm) often has excellent physical and chemical properties, generally has high strength, hardness, fatigue life and low temperature superplasticity, high strain rate and excellent cutting properties and other comprehensive mechanical properties, some materials also have good thermal stability, corrosion resistance, wear resistance and biological properties. At present, the processing of ultrafine crystalline metal materials mainly includes physical deposition, rapid solidification, amorphous crystallization, mechanical alloy method and extrusion, rolling, drawing and other methods of strong and large plastic deformation. Among them, strong plastic deformation method (SPD, mainly including equal diameter Angle extrusion (ECAP), cumulative composite rolling (ARB), etc.) has attracted wide attention due to its strong grain refining ability, not easy to introduce micro-pores and impurities, and can prepare large-size massive samples. This method points out a new direction for the optimization and upgrading of mechanical properties of traditional medical metal materials. It is also the best way to solve the problems of low strength, high modulus and poor biomechanical properties of medical pure titanium.
Ti-6Al-4V and Ti-6Al-4VELI finely crystallized rods and wires with diameters of 0.5~20 mm were processed by cumulative large deformation cold rolling technology. The grain structure ratings were all A1, and the strength and plasticity indexes were better than those of the same industrial coarse crystalline titanium alloy materials. Subsequently, the team uses an improved ARb-cumulation-rolled technique to fabricate new high-strength and low-modulus β titanium alloy TLM ultra-fine crystal sheets and foil, and systematically study their microstructure and mechanical properties. The study [73] found that with the increase of the number of composite layers, the internal dislocation density of the ultra-fine crystal sheet increased, the proportion of ultra-fine grains increased, the yield strength, tensile strength and surface hardness gradually increased, and the elastic modulus showed an overall upward trend. Eight layers of thin sheet are uniformly distributed with superfine grains with grain size of about 100 nm and surrounded by obvious grain boundaries. The maximum tensile strength is 1200 MPa, which is 49% higher than that of single layer cold rolled sheet. The 16-layer composite plate is full of ultrafine crystal structure, and the average grain size is about 50 nm.
