Fabrication of Ceramic-Metal Functionally Graded Materials

Abstract

High order step wise functionally graded materials Al 2 O 3-Ti are fabricated. These materials combine the high fracture toughness of Ti phase and the relatively low density of Al 2 O 3 and stand for candidate materials for harsh mechanical and thermal environments. The techniques of powder technology are utilized to fabricate these materials that composed of five graded layers of Al 2 O 3-Ti phases. Al 2 O 3 increasing linearly across these layers (0, 25, 50, 75 and 100wt% respectively). The green specimens are composed of Al 2 O 3-TiH 2 layers and the sintered specimens are composed of graded Al 2 O 3-Ti. Spark Plasma Sintering technique is utilized for sintering of the graded green specimens. The best sintering conditions is found at 1500°C for 30 minute of sintering that gives apparent density of 4.25 g/cm 3 , porosity of 1.28% and diametric expansion of 1.58%. Optical microscopy shows gradual transition of phases at the interface of the graded layers. Keywords: Functionally graded materials, Spark plasma sintering. ‫ﻟـ‬ ‫ﻭﻅﻴﻔﻴﺎ‬ ‫ﺍﻟﻤﺘﺩﺭﺠﺔ‬ ‫ﺍﻟﻤﻭﺍﺩ‬ ‫ﺘﺤﻀﻴﺭ‬) ‫ﺴﻴﺭﺍﻤﻴﻙ‬-‫ﻓﻠﺯ‬ (‫ﺍﻟﺨﻼﺼ‬ ‫ــــ‬ ‫ﺔ‬ ‫ﺘﻡ‬ ‫ﻤﻥ‬ ‫ﻤﺘﺩﺭﺠﺔ‬ ‫ﻤﻭﺍﺩ‬ ‫ﺘﺼﻴﻨﻊ‬ Al 2 O 3-Ti ‫ﻋﺩﻴﺩﺓ‬ ‫ﻤﺘﺴﻠﺴﻠﺔ‬ ‫ﺒﻁﺒﻘﺎﺕ‬. ‫ﻤﻘﺎﻭﻤـﺔ‬ ‫ﺒـﻴﻥ‬ ‫ﺍﻟﻤـﻭﺍﺩ‬ ‫ﻫﺫﻩ‬ ‫ﺘﺠﻤﻊ‬ ‫ﻟﻁﻭﺭ‬ ‫ﺍﻟﻌﺎﻟﻴﺔ‬ ‫ﺍﻟﻜﺴـﺭ‬ Ti ‫ﻟﻁﻭﺭ‬ ‫ﻨﺴﺒﻴﺎ‬ ‫ﺍﻟﻤﻨﺨﻔﻀﺔ‬ ‫ﻭﺍﻟﻜﺜﺎﻓﺔ‬ Al 2 O 3 ‫ﻓﻲ‬ ‫ﻤﻨﺎﻓﺴـﺔ‬ ‫ﻜﻤﻭﺍﺩ‬ ‫ﺍﻟﻤﻭﺍﺩ‬ ‫ﻫﺫﻩ‬ ‫ﻭﺘﺭﺸﺢ‬ ‫ﻭﺍ‬ ‫ﺍﻟﻤﻴﻜﺎﻨﻴﻜﻴﺔ‬ ‫ﺍﻟﻅﺭﻭﻑ‬ ‫ﺍﻟﻘﺎﺴـﻴﺔ‬ ‫ﻟﺤﺭﺍﺭﻴﺔ‬. ‫ﻤـﻥ‬ ‫ﻭﺍﻟﻤﺅﻟﻔﺔ‬ ‫ﺍﻟﻤﻭﺍﺩ‬ ‫ﻫﺫﻩ‬ ‫ﻟﺘﺼﻨﻴﻊ‬ ‫ﺍﻟﻤﺴﺎﺤﻴﻕ‬ ‫ﺘﻘﻨﻴﺎﺕ‬ ‫ﺍﺴﺘﺨﺩﺍﻡ‬ ‫ﺘﻡ‬ ‫ﺍﻻﻁﻭﺍﺭ‬ ‫ﺒﻨﺴﺏ‬ ‫ﻤﺘﺩﺭﺠﺔ‬ ‫ﻁﺒﻘﺎﺕ‬ ‫ﺨﻤﺴــﺔ‬ Al 2 O 3-Ti. ‫ﺍﻟﻁـﻭﺭ‬ ‫ﻨﺴــﺒﺔ‬ ‫ﺘﺘﺯﺍﻴﺩ‬ Al 2 O 3 ‫ﺨـﻼل‬ ‫ﺨﻁﻴـﺎ‬ ‫ﺍﻟﻁﺒﻘﺎﺕ‬) 0 ، 25 ، 50 ‫ﻭ‬ ، 100wt% ‫ﺍﻟﺘﻭﺍﻟﻲ‬ ‫ﻋﻠﻰ‬ .(‫ﻤﻥ‬ ‫ﻁﺒﻘﺎﺕ‬ ‫ﻤﻥ‬ ‫ﺍﻟﺨﻀﺭﺍﺀ‬ ‫ﺍﻟﻨﻤﺎﺫﺝ‬ ‫ﺘﺘﻜﻭﻥ‬ Al 2 O 3-TiH 2 ‫ﺒ‬ ‫ﺍﻟﻨﻤﺎﺫﺝ‬ ‫ﻭﺘﻜﻭﻥ‬ ‫ﺘـﺩﺭﺝ‬ ‫ﻤﻥ‬ ‫ﻤﻜﻭﻨﺔ‬ ‫ﺍﻟﺘﻠﺒﻴﺩ‬ ‫ﻌﺩ‬ ‫ﻤﻥ‬ Al 2 O 3-Ti. ‫ﺍﻟﺒﻼﺯﻤﺎ‬ ‫ﺒﺸﺭﺍﺭﺓ‬ ‫ﺍﻟﺘﻠﺒﻴﺩ‬ ‫ﺒﺎﺴﺘﺨﺩﺍﻡ‬ ‫ﺍﻟﺨﻀﺭﺍﺀ‬ ‫ﺍﻟﻤﺘﺩﺭﺠﺔ‬ ‫ﺍﻟﻨﻤﺎﺫﺝ‬ ‫ﺘﻠﺒﻴﺩ‬ ‫ﺘﻡ‬. ‫ﺃﻓﻀـل‬ ‫ﺍﻥ‬ ‫ﻭﻭﺠﺩ‬ ‫ﺍﻟﺘﻠﺒﻴﺩ‬ ‫ﺤﺭﺍﺭﺓ‬ ‫ﺩﺭﺠﺔ‬ ‫ﻓﻲ‬ ‫ﻫﻲ‬ ‫ﻟﻠﺘﻠﺒﻴﺩ‬ ‫ﻅﺭﻭﻑ‬ 1500°C ‫ﺘﻠﺒﻴـﺩ‬ ‫ﻟﺯﻤﻥ‬ 30 ‫ﻜﺜﺎﻓـﺔ‬ ‫ﺍﻟـﻰ‬ ‫ﺍﺩﻯ‬ ‫ﻭﺍﻟـﺫﻱ‬ ‫ﺩﻗﻴﻘـﺔ‬ ‫ﺒﻤﻘﺩﺍﺭ‬ ‫ﻀﺎﻫﺭﻴﺔ‬ 4.25 g/cm 3 ‫ﺒﻤﻘﺩﺍﺭ‬ ‫ﻭﻤﺴـــﺎﻤﻴﺔ‬ 1.28% ‫ﻭﺘ‬ ‫ﺒﻤﻘـﺩﺍﺭ‬ ‫ﻗﻁﺭﻱ‬ ‫ﻤﺩﺩ‬ 1.58%. ‫ﻭﻗـﺩ‬ ‫ﺍﻟﻤﺘﺩﺭﺠﺔ‬ ‫ﺍﻟﻁﺒﻘﺎﺕ‬ ‫ﺒﻴﻥ‬ ‫ﺍﻟﺤﺩﻭﺩ‬ ‫ﻋﻠﻰ‬ ‫ﻟﻼﻁﻭﺍﺭ‬ ‫ﻤﺘﺩﺭﺝ‬ ‫ﺘﺤﻭل‬ ‫ﺍﻟﻀﻭﺌﻲ‬ ‫ﺍﻟﻤﺠﻬﺭ‬ ‫ﻓﺤﻭﺼﺎﺕ‬ ‫ﺍﻅﻬﺭﺕ‬. INTRODUCTION uch research and development have been carried out to develop Functionally Graded Materials FGMs for various applications using gradients in physical, chemical, biochemical, and mechanical properties. The main characteristic that distinguishes FGMs from conventional composite materials is the tailoring of graded composition and microstructure in an intentional manner. That gradation aimed to design the distribution of properties needed to achieve the desired function. The majority of FGMs design case the integration of incompatible functions of the refractoriness and wear resistance of ceramics in one side and the toughness of metals on the other side; which found various structural applications [1]. FGM s that are made from a mixture of metal and ceramics are typically characterized by smooth and continuous change of the mechanical properties from one side to another. These FGM s designs are reported to overcome weakness of the laminated composite materials; such as de-bonding at massive stress or local large plastic deformations [2]. Another case study is the fabrication of metal-ceramic joints; where cracking are often occurs during the buildup of residual stresses caused by the large difference in thermal expansion between metal and ceramic components. FGM designs proofs excellent solution in such cases as a result of the spatial variation in composition. That gradation in composition keeps the thermo-mechanical stresses within acceptable limits and minimizes the residual thermal stresses [3]. Generally, the compositional gradient obtainable by the functionally graded materials FGM s offer a solution for problems arises from the existence of sharp interfaces by tolerating continuous transition from one material property to the another property avoiding abrupt mismatch [4]. Nevertheless, the synthesis if a gradient material is a challenge itself. A process design stage should be accomplished for synthesis of gradient material. Thus, a wide variety of available processes have been reported for the synthesis of FGMs; such as plasma spraying, centrifugal casting, powder technology, PVD, CVD, and colloidal processing. Amongst these processes, electrophoretic deposition (EPD) is a fairly rapid low cost process, capable of manufacturing continuously graded materials with complex geometry [5]. The powder technology process proofs flexible and suitable route for FGM fabrication. A common practice is to build-up of the graded structure by a stepwise composition of precursor materials or powders. The manufacturing process of a FGM can usually be divided in two major steps. The first step is the construction of spatially distributed structure of constituent materials which is called the gradation. Then, transform to bulk material via the consolidation of the constituents by e.g. an appropriate sintering process [6]. An emerged sintering technique called Spark Plasma Sintering SPS gains much attention in the scientific community. A pulsated electrical energy is provided to the powder compact which is momentarily energize it and generates spark plasma. Thus, sinter bonding of the particles is stimulated across the compact. Repetitive pulses in the course of 5 to 20 minutes accomplish sintering including temperature