Sintering of Powdered Copper Brendan Short, Brendan Barrett, Jason Gamble Engineering 45, SRJC Fall 2011

Sintering Overview  What is Sintering?  How does Sintering Work?  What Materials can be Sintered?  What are the advantages of sintering?

What is Sintering  Sintering is a metallurgical process in which a powdered material is compressed and heated to form a solid part in the desired shape In more detail: Solid state sintering is the process of taking metal in the form of a powder and placing it into a mold or die. Once compacted into the mold the material is placed under a high heat for a long period of time. Under heat, bonding takes place between the porous aggregate particles and once cooled the powder has bonded to form a solid piece. Sintering can be considered to proceed in three stages. During the first, neck growth proceeds rapidly but powder particles remain discrete. During the second, most densification occurs, the structure recrystallizes and particles diffuse into each other. During the third, isolated pores tend to become spheroidal and densification continues at a much lower rate. The words Solid State in Solid State Sintering simply refer to the state the material is in when it bonds, solid meaning the material was not turned molten to bond together as alloys are formed.[11] One recently developed technique for high-speed sintering involves passing high electrical current through a powder to preferentially heat the asperities. Most of the energy serves to melt that portion of the compact where migration is desirable for densification; comparatively little energy is absorbed by the bulk materials and forming machinery. Naturally, this technique is not applicable to electrically insulating powders. To allow efficient stacking of product in the furnace during sintering and prevent parts sticking together, many manufacturers separate ware using Ceramic Powder Separator Sheets. These sheets are available in various materials such as alumina, zirconia and magnesia. They are also available in fine medium and coarse particle sizes. By matching the material and particle size to the ware being sintered, surface damage and contamination can be reduced while maximizing furnace loading. Source: Todd, Robert H., Allen, Dell K., Alting, Leo, "Manufacturing Processes Reference Guide", 1st Edition, Industrial Press Inc., New York 1994, ISBN ISBN

How Does Sintering Work?  Sintering works by atomic diffusion of powdered materials which is greatly accelerated at high temperatures In more detail: Sintering is a method used to create objects from powder. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature below the melting point. The atoms in the powder particles diffuse across the boundaries of the particles, fusing the particles together and creating one solid piece. Because the sintering temperature does not have to reach the melting point of the material, sintering is often chosen as the shaping process for materials with extremely high melting-points such as tungsten and molybdenum.tungstenmolybdenum Source: "Materials Science and Engineering: R: Reports : Consolidation/synthesis of materials by electric current activated/assisted sintering". ScienceDirect. Retrieved "Materials Science and Engineering: R: Reports : Consolidation/synthesis of materials by electric current activated/assisted sintering"

What Can be Sintered?  Most Metals, Ceramics, and Plastics In more detail: Most, if not all, metals can be sintered. This applies especially to pure metals produced in vacuum which suffer no surface contamination. Sintering under atmospheric pressure requires the usage of a protective gas, quite often endothermic gas. Many nonmetallic substances also sinter, such as glass, alumina, zirconia, silica, magnesia, lime, ice, beryllium oxide, ferric oxide, and various organic polymers. Sintering, with subsequent reworking, can produce a great range of material properties. Changes in density, alloying, or heat treatments can alter the physical characteristics of various products. For instance, the Young's Modulus E n of sintered iron powders remains insensitive to sintering time, alloying, or particle size in the original powder, but depends upon the density of the final product: Plastic materials are formed by sintering for applications that require materials of specific porosity. Sintered plastic porous components are used in filtration and to control fluid and gas flows. Sintered plastics are used in applications requiring wicking properties, such as marking pen nibs. Sintered ultra high molecular weight polyethylene materials are used as ski and snowboard base materials. The porous texture allows wax to be retained within the structure of the base material, thus providing a more durable wax coating. Source: "Materials Science and Engineering: R: Reports : Consolidation/synthesis of materials by electric current activated/assisted sintering". ScienceDirect. Retrieved "Materials Science and Engineering: R: Reports : Consolidation/synthesis of materials by electric current activated/assisted sintering"

What are the advantages of Sintering  Very high and uniform purity can be easily achieved  The simple fabrication process retains purity  Grain size is easily controlled  No deformation is needed to produce directional elongation of grains  Void density can be controlled  Objects can be created in any shape  Shapes can be produced that not be made by any other process

Project Materials and Preparation  99.63% atomized pure copper powder with spherical particles with a range of sizes from 45 to 75 micrometers was used  Hydraulic Press  Cylindrical Mold  High Temperature Ovens  Ceramic Oven Cups  Microscope with digital imaging  Polishing and sanding tools  Scale  Gloves and protective eyewear  Bandages for Younes

Project Procedure 1.Weigh out 10 gram amounts of copper powder for pellets 2.Copper powered compressed to cylindrical pellets under 10,000 psi with hydraulic press 3.Samples put into ovens at temperatures of 900 and 1500 degrees Fahrenheit 4.Samples pulled from oven at 10 minutes (only 1500 degree), 30 minutes, 60 minutes, 90 minutes (only 900 degree), and 6 hours 5.Samples sanded, polished, and examined under microscope at 40x lens magnification and 30x camera magnification for around 1200x total magnification

Project Results:  Photographs of Un-sintered copper pellets  Photographs of 900 degree sintered copper  Photographs of 1500 degree sintered copper  Our Results Clearly show the diffusion of the copper particles over time Oxidation on a Sample

Non-Sintered Copper

900 Degrees for 30 minutes

900 Degrees for 60 minutes

900 Degrees for 90 minutes

900 Degrees for 6 Hours

1500 Degrees for 10 min

1500 Degrees for 30 min

1500 Degrees for 1 hour

1500 Degrees for 6 hours

900 Degree Progression 30 min 60 min 90 min 6 hr

1500 Degree Progression 10 min 30 min 60 min 6 hr

Expected Results:

References: "Materials Science and Engineering: R: Reports : Consolidation/synthesis of materials by electric current activated/assisted sintering""Materials Science and Engineering: R: Reports : Consolidation/synthesis of materials by electric current activated/assisted sintering". ScienceDirect. Retrieved Todd, Robert H., Allen, Dell K., Alting, Leo, "Manufacturing Processes Reference Guide", 1st Edition, Industrial Press Inc., New York 1994, ISBN ISBN “The Ultimate Source for Information on Copper and Copper Alloys” Mepco (The Metal Powder Company Limited) Materials Safety and Information Sheet