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Support-Free Infiltration of Selective Laser Sintered (SLS) Silicon Carbide Preforms
Non-metallic objects are often difficult to manufacture due to high melting temperatures,
poor sinterability, limited ductility, and difficulty in machining. Freeform fabrication techniques
coupled with liquid infiltration offer a cost-effective and rapid manufacturing mechanism for
composite parts with complex geometry and adequate properties. Selective laser sintered (SLS)
silicon carbide (SiC) preforms infiltrated with liquid silicon develop localized infiltrant overextrusions onto surfaces and at surface irregularities. Several shrinkage mechanisms including
densification were studied as possible causes of these overfilling extrusions, and the results are
discussed below. This research was supported by NSF Grant Number DMI-0522176.Mechanical Engineerin
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SLS Materials Development Method for Rapid Manufacturing
As soon as SFF technology development began to make Rapid Prototyping possible the
interest in Rapid Manufacturing (RM) began to grow. The advantages in terms of
functional integration, elimination of tooling and fixtures and mass customization make a
compelling case for RM, leading some in the field to call it the next industrial revolution.
Yet without the materials properties necessary to provide the function and variety
currently available from mass production methods, the application of RM will remain
limited. Developing new materials for the SLS process, one immediate step toward a
larger portfolio of RM materials, is very challenging. The formation of high quality SLS
parts relies on appropriate powder characteristics, thermal cycles and sintering behavior.
Based on a brief examination of the key factors in SLS processing and a research project
to develop a new binder material for Silicon Carbide composites, a systematic materials
development method is proposed in this paper. The method provides guidance for
introducing new SLS materials, support for educating new SLS users and researchers and
direction for several future research projects.Mechanical Engineerin
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Rapid Manufacturing of Silicon Carbide Composites
From the earliest days of SFF technology development, a viable technique for the direct
manufacture of fully-functional parts has been a major technology goal. While direct metal
methods have been demonstrated for a variety of metals including aluminum, steel and titanium,
they have not reached wide commercial application due to processing speed, final material
properties and surface finish. In this paper the development of an SLS-based rapid
manufacturing (RM) platform is reviewed. The core of this platform is a thermosetting binder
system for preform parts in contrast to the thermoplastic materials currently available for SLS.
The preforms may include metal and/or ceramic powders. A variety of fully functional parts
can be prepared from different combinations of materials and post processing steps including
binder pyrolysis, free-standing alloy infiltration, room temperature polymer infiltration and
machining. The main issues of these steps are reviewed followed by a discussion about the
support of RM. This paper is an intermediate report additional materials, applications, process
models and product design strategies will be incorporated into the project in the next year.Mechanical Engineerin
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Negative priming in free recall reconsidered
Recent investigations of the phenomenon of forgetting have been driven mostly by the development of a novel theoretical framework which places great emphasis on inhibitory control (Anderson, 2003; Anderson & Spellman, 1995; Bjork, 1989). Whereas traditional, interference-based theories consider forgetting to be a by-product of storing new information, the inhibitory framework postulates a specialized mechanism, or a group of mechanisms, that serves the function of âdeactivatingâ information which is currently irrelevant. This process of inhibiting currently irrelevant information is thought to have lasting consequences, affecting memory for the irrelevant information on subsequent tests. The active and functional perspective on forgetting embedded in the inhibitory framework opens new fields for examining the role of forgetting in cognitive functioning. Differences in the ability to inhibit irrelevant information have been postulated to play important roles in a range of clinical conditions (e.g., Soriano, JimĂ©nez, RomĂĄn, & Bajo, 2009; Storm & White, 2010) and the trajectory of cognitive development (e.g., Aslan & BĂ€uml, 2010) as well as contributing to individual differences in many other cognitive and social domains (Redick, Heitz, & Engle, 2007)
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Selective Laser Sintering of High Performance High Temperature Materials
Hot Isostatic Pressing (HIP) of high performance metal parts is currently done using either a shaped
metal container or a pre-fabricated ceramic mold depending on the part material and geometry. An
alternative method of HIP encapsulation that allows complex part geometry, short cycle time and
minima) potential for container-powder bed interaction is desired. Integral, fully dense metal skins
with complex geometry can potentially be constructed by direct selective laser sintering (SLS). The
advantages ofin-situ HIP encapsulation by direct SLS include the elimination of a secondary container
material and any associated container-powder bed interaction, reduced pre-processing time and a short
HIP cycle. Single and multi-layer specimens of Inconel625, Ti-6AI-4Vand 17-4 PH stainless steel
were produced by direct SLS. Closed porosity in Inconel625 and 17-4 PH stainless steel samples
ranged from 0 to 12% and area porosity from 0.5 to 20%, depending on the laser energy density.
Direct SLS samples ofInconel 625 were subjected to helium leak testing and found to be impervious,
with a leak rate less than lxl0-10 atm eels. These samples met the criteria for containerless hot
isostatic pressing.Mechanical Engineerin
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