ECAE (equal channel angular extrusion) based preparation method of ultrafine crystal NiTi shape memory alloy tube

Abstract

The invention provides an ECAE (equal channel angular extrusion) based preparation method of an ultrafine crystal NiTi shape memory alloy tube. A metal core is inserted into a NiTi shape memory alloy tube blank to be shaped, then the NiTi shape memory alloy tube blank is enclosed in a metal covering, and the metal covering, the NiTi shape memory alloy tube blank and the metal core are simultaneously extruded to generate shear plastic deformation in an ECAE production tool consisting of male die and a female die, so as to realize grain refinement of the NiTi shape memory alloy tube blank. Based on the fundamental of the ECAE method, a preparation method of an ultrafine crystal NiTi shape memory alloy tube is provided by the invention, so that high quality ultrafine crystal NiTi shape memory alloy tube can be produced, and production costs of the ultrafine crystal NiTi shape memory alloy tube can be reduced substantially.

Description

technical field [0001] The invention relates to a method for preparing an ultrafine crystal tube material, in particular to a method for preparing an ultrafine crystal nickel-titanium shape memory alloy tube material based on an equal-diameter angular extrusion technique. Background technique [0002] Since the appearance of nickel-titanium shape memory alloy tubes in the 1990s, people have paid more and more attention to them in the field of medical applications, especially in the application of interventional endoluminal stents, because they can withstand greater mechanical stress and have stronger diameters. It exhibits good application prospects because of its strong lateral support, greater bending deformation, and greater resilience and shape recovery. Although nickel-titanium shape memory alloy pipes can be manufactured by a variety of processing methods, different processing conditions will affect the microstructure of nickel-titanium shape memory alloy pipes (such a...

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Problems solved by technology

However, the current ECAE technology can generally only be used to prepare bulk materials (circular or rectangular cross-sections) with ultrafine grains, and cannot directly prepare pipes with ultrafine grains.

Although the publication number is CN2690068Y in the patent literature, a kind of device for preparing ultra-fine grain pipe material is proposed, because the device has a mandrel, the fixing of the mandrel is difficult to realize during the specific implementation, thus the equipment Higher requirements must be carried out on a dedicated extruder

Moreover, since the inner angle φ and the outer angle ψ of the mold are inconsistent during equal-diameter angular extrusion, the structure of the tube blank obtained by one-pass forming is bound to be uneven, and it must be formed by multi-pass extrusion to have a uniform structure. The outer surface of the blank is a cylindrical surface, and it is difficult to accurately determine the position of each pass when the direction is changed, so it is difficult to ensure a uniform structure

In addition, because nickel-titanium shape memory alloys have high strength, strong hardening ability, and poor plasticity at relatively low temperatures, the equal angular extrusion of bulk nickel-titanium shape memory alloy materials has high requirements for equipment. When the crystalline nickel-titanium shape memory alloy bulk material is used to prepare ultra-fine-grained nickel-titanium shape memory alloy tubes, the production cost will be greatly increased

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