Yielding behavior of low expansion invar alloy at elevated temperature

An invar alloy is used for a shadow mask in a color picture or display tube (CPT or CDT) for its low coefficient of thermal expansion, but in practice distortion or deformation of the shadow mask sometimes occurs after mold-p ressing formation. This implies that the formation facilities and parameter s do not conform with the mechanical response of the material, and that the mechanical performance of the material has not yet been clearly understood using strain gages, tensile tests were carried out at elevated temperature s to determine the yielding behavior of the invar alloy. The main results s how that the yield stress decreases by 55% with increasing heating temperat ure from about 20 to 180 degreesC and then remains stable at 120-130 MPa fo r 180-220 degreesC for specimens pre-annealed at temperatures ranging from 790 to 850 degreesC. The plastic elongation at the same time increases with the annealing and heating temperatures. Thus, the pressing force and defor mation temperatures can be evaluated as important parameters controlling th e formation of the shadow mask (C) 2001 Elsevier Science B.V. All rights re served.