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Precision alloys with set elasticity properties
Main information
Precision alloys with set elasticity properties - alloys with high stability towards slight plastic deformations and relaxation resistance under static and cyclic loads; they are used as springs and spring elements, elastically sensitive elements of instruments, diaphragms of flow meters, resonators of filters for choosing, generating and tuning for a set frequency.
Relaxation resistance - a material ability to resist relaxation (e.g., stress); relaxation - self-active load damping fall within time that occurs due to transition of elastic deformation into plastic deformation. Typical relaxation example - reduction of tension of bolts and studs in flange connections. Although the bolts are initially tightened, they get loosened due to the partial transition of elastic deformation into plastic deformation under high temperatures. These materials are based on several systems:
Classification
Precision alloys with set elasticity properties can be conditionally divided by hardening form and physico-mechanical properties.
Properties
Precision materials with set elasticity properties should comply with the following requirements: they should have a high or, vice versa, low modulus of elasticity, low temperature coefficient of the modulus of elasticity, high quality factor, low elastic hysteresis (in the theory of elasticity hysteresis occurs in elastic materials that can maintain deformation under high pressure and lose it under return pressure (e.g., stretching of the fixed column)), elastic time-effect, high fatigue limit, corrosive stability, non-magnetization, electric conductivity, wear resistance and stability of these properties under operation temperatures. These materials should have a process plasticity for making elastic elements with a set configuration and weldability.
Grades
The main grades of precision alloys of the considered class are given in Classification section, Table 1. The chemical composition and other requirements are regulated by GOST 10994-74.
Applications
Products made of precision alloys with set elasticity properties are used in many industries: production of elastic sensitive elements, sensors; different types of springs, medical tools.
Precipitation hardening alloys are applied for making the following products: elastic sensitive elements working within -250-400 °С depending on the certain material grade; pressure gauges working within -253-250 °С; power and belleville springs used in underground well equipment for extracting natural gas containing hydrogen sulphide. Also some grades can be applied as corrosive construction materials. Deformation-hardening materials are used in heat-resistant springs and mainsprings; centerpunches of electric-measuring instruments; geodesic and gyroscopic devices (for elastic elements in micron sections); flat diaphragms; elastic torque members working under high temperatures in vacuum or inert gases and hydrogen. Alloys with a thermally stable modulus of elasticity are widely applied in instrument engineering for producing elastic sensitive elements of ultrathin instrumentation and controls without temperature control and compensation. They are used for making haircoils and hair of special clockworks, flat, coil and helical springs, resonators of electromechanical filters, aneroid chambers, bellows boots, acoustic ducts, Bourdon tubes, engine speed controllers, pressure gauges. Elastic alloy application in medicine is worth mentioning individually. Biocompatibility is the general requirement towards materials used in medical equipment (especially to those implanted into the human body). The materials should not cause clots or inflammations and should have the required mechanical properties (elasticity, fatigue strength, etc). 36NiCrTiAl grade is used for entry needles made of thin-wall tubes with diameter 0.8-2.0 mm. 40CoCrNiMo alloy is applied for clamps for stitching vessels, prosthetic repair of the eye-ball stump, for bone surgery in orthopedics - “pegs” for bone fastening, joint prostheses, for wound springs used for bone union under pressure; for short-term cardiac activation, etc. 40Co27CrNiMo grade with Та has a higher corrosive stability in the human body and saline solution than 40CoCrNiMo alloy. The main applications are electrodes for long-term and continuous activation of tissues and organs (heart, brain, bladder, gastrointestinal tract, etc.) made of wire with diameter 0.15-0.2 mm with 30-40% deformation. Besides that, the wire of this alloy is used for making acupuncture needles, elastic corrective facilities applied in surgery for treating spinal curvature and bone ruptures so as correcting the lower limb axis. Strips 0.13-0.15 mm thick with 30-40% deformation are used for making anti-thrombotic filters. A softened hot-rolled sheet 5-12 mm thick and wire with diameter 0.9-1.1 mm and 30-40% deformation are used for making frames of artificial heart valves. 40CrNiAl-WI alloy is used for making general surgical lancets due to high wear resistance and corrosive stability. Such lancets have better operational properties than mass-produced steel lancets. Products
Materials with set elasticity properties are produced in form of flat (strips, flat bars and sheets) and round products (wire, rods and pipes). The certain application determines the use of the blanks.
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