NiTinol Heat Treatment & Shape Memory
ANV Laser provides the following Nitinol heat treatment and other thermal treatment services:
- NiTi shape setting
- NiTi Af setting
- CoCr and Ti annealing in vacuum and air
Heat treatments are used to form the final shape of a component and/or to stabilize the material properties of the metals and metal alloys from which it has been produced.
ANV Laser often produces precision components from Nitinol (NiTi)− a nickel-titanium alloy that was discovered in the early 1960s. NiTi has remarkable shape-memory and super-elastic properties in comparison with conventional engineering alloys. These material properties and its biocompatibility have made NiTi the alloy of choice for medical devices in general and for implanted devices in particular, such as heart valves, stents, vena cava filters, etc.
NiTi Shape Setting
Nitinol (NiTi)’s outstanding shape-memory and super-elasticity properties make it ideal for shape setting to meet the most complex geometric or anatomical requirements. We set the shape during several Nitinol heat treatment and cooling cycles carried out in succession, the last of which determines the final shape of the component. The Nitinol heat treatment takes place in our specialized fluidized baths while the component is constrained on a stainless steel mandrel or jig that we design and produce ourselves. 3D-printed CoCr mandrels/jigs are also available upon special request.
It requires extensive experience and expertise to determine the number of required cycles and the optimal heating/cooling profiles that will achieve the desired shape without losing the special mechanical properties of the Nitinol. If not done properly there can be localized areas in the component where the shape-memory and super-elasticity properties have been changed, with adverse effects on performance such as poor fatigue resistance.
NiTi Af Setting
A successful NiTi application also requires precise control of its transformational properties. The Austenite finish (Af) temperature, for example, is the temperature at which the transformation from martensite to austenite finishes and the material will be in its super-elastic state. It is important, therefore, that a component’s Af temperature will be below the temperature at which the product will be used.
After the component’s shape has been set, we can also set its Af temperature(if necessary) through a precisely controlled thermal treatment in a specialized furnace.
For our own quality control purposes we have developed the NCAT (Non Contact Af Tester) that can test the Af temperature of several devices, of different shapes, at the same time.
CoCr and Ti Annealing in Vacuum and in Air
Annealing is a heat treatment that alters the microstructure of a material and causes changes in properties such as strength, hardness, and ductility. Annealing is typically carried out in order to soften the metal, to increase its fatigue strength and to relieve internal stresses introduced during the laser cutting stage – stresses that could ultimately cause microfractures in the finished product.
Performing annealing under vacuum conditions prevents oxidation of the component.