Injection molding of ultra-fine Si3N4 powder for gas-pressure sintering

Yang, Xianfeng; Yang, Jianghong; Xu, Xiewen; Liu, Qicheng; Xie, Zhihui; Liu, Wei

doi:10.1007/s12613-015-1119-6

Cited by 16 publications

(5 citation statements)

References 24 publications

(22 reference statements)

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“…Debinding coefficient could be augmented with the adoption of elevated temperature, where molecular vibrations are stimulated. During the first stage, the control of the debinding process was carried out by the dissolution of binder at the debinding interface, agreeing with debinding dynamic analysis; consequently, control was transferred to the diffusion of binder in the connected pores of the outer layer in debinding state, with the increase in the debinding depth [11]. However, an adequately extended debinding period was essential due to the prerequisite of the following thermal debinding, which could only be done when an enough quantity of binder was solvent in the debinding state for the formation of connected pore nets in the green body.…”

Section: Resultsmentioning

confidence: 70%

“…Subsequently, a sintering process is done for the porous products to a density near the theoretical required one. Debinding is a critical core step in eliminating large fraction of the organic phase, in which defects such as cracking, bloating, or deforming is avoided [11][12]. Thermal debinding is the first and the most common utilized method in the PIM industry, due to its simplicity and low equipment investment.…”

Section: Introductionmentioning

confidence: 99%

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Comparative study of different alloys during thermal debind-ing of powder injection molded parts

El-Garaihy

Nassef

El-Hadek

2016

IJET

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Powder injection molding (PIM) is an interesting technique and address of research, in which a thermoplastic polymeric material is used to form the powder into the desired shape in a closed die. Binders have a crucial importance in the powder metallurgy technology as they play a vital role to provide efficient powder agglomeration and/or lubrication during shaping. At the same time, they have to be easily removed from the compacts during initial stages of sintering, using debinding process, without any damaging effect for the base material. Thermal debinding is a vital process requiring somewhat elevated temperatures to remove binder from the compact. In the current study, an investigation has been made about the effect of process variables on the debinding of injection molded pieces, by melt wicking. The debinding process was performed at temperatures ranging from 160-up to-200°C for a time duration varying from 1-up to-27 hours. All powders used in injection molding feedstock have an inherent packing porosity. Several types of alloy powders (Carbonyl iron steel, Nickel aluminide, and 316L stainless powders), with various size distributions, particle shapes, and materials are adopted to define the influence on binder incorporation resulted from this inherent porosity. Results revealed that the increase of debinding time or decrease in the wicking powder (alumina) particle size lead to an increase in the thickness of the adhered layer of alumina. When the wicking powder is very fine (0.3 m) or has a wide particle size range (<10 m), it becomes more dense and its debinding efficiency is decreased. At high debinding temperatures (200 °C) the rate of binder evaporation and removal increased, which leads to decreasing the cohesion of the samples yielding a shape distortion. In addition, the effect of the wicking powder (Al 2 O 3 ) sizes and debinding time on the binder weight loss percentage after debinding process for FeOX, Ni 3 Al, and 316L has been investigated.

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Section: Resultsmentioning

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Comparative study of different alloys during thermal debind-ing of powder injection molded parts

El-Garaihy

Nassef

El-Hadek

2016

IJET

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“…The hardness values range from 9.7 to 18.4 GPa, for Si 3 N 4 ceramic sintered between 1400 and 1750°C. Yang et al [32]. obtained a hardness of 16.5 HV for a low pressure-assisted silicon nitride sintering at 1800°C.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

HPHT sintering of binderless Si3N4: structure, microstructure, mechanical properties and machining behavior

Filgueira

Nascimento

Oliveira

et al. 2018

J Braz. Soc. Mech. Sci. Eng.

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Silicon nitride (Si 3 N 4) is widely used in the manufacture of cutting tools due to the combination of properties such as high hardness, fracture toughness and wear resistance. This ceramic is usually sintered by liquid phase, causing the reduction of thermo-mechanical properties. This work investigated the sintering of pure (binderless) Si 3 N 4 tools by a high pressure and high-temperature (HPHT) technology. Sub-micrometric a-Si 3 N 4 powder was hot-pressed at 1700°C for 3 min, using extreme pressures of 5, 6 or 7 GPa. The sintered samples were characterized by XRD and atomic force microscopy (AFM); hardness and fracture toughness were measured by the indentation fracture method (IF). Preliminary machining tests with binderless-Si 3 N 4 tools were performed using AISI 4140 hardened steel. Commercial TiN-coated hard metal insert was used as a comparative tool material. Turning tests were carried out using coolant/lubricant, cutting time of 12 min, cutting speed of 150 m/min, cutting depth of 0.3 mm and feed of 0.11 mm/rev. The results showed the presence of a-Si 3 N 4 and b-Si 3 N 4 crystalline phases after sintering, indicating partial a ? b phase transformation, with elongated b-Si 3 N 4 grain. The relative density after sintering was near 90-97%. The best results for the mechanical properties were hardness of 21 GPa and fracture toughness of 8.9 MPa m 1/2. The machining results indicated an improvement on surface quality when using Si 3 N 4 ceramic tool. The flank wear of the hard metal insert was 0.7 mm, while the wear of binderless Si 3 N 4 insert was substantially lower, 0.1 mm. The roughness (R a) measured in AISI 4140 steel was 17.6 lm (HPHT Si 3 N 4 insert) and 19.7 lm (TiN-coated hard metal insert), after machining tests. Keywords Si 3 N 4 ceramics Á High-pressure and high-temperature (HPHT) Á Mechanical properties Á Machining

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“…Though a lot of advanced technologies (solvent debinding, wick‐debinding, supercritical debinding, microwave debinding, catalytic debinding etc. ) have been developed, thermal debinding is still the most widely employed method. Because, the process of thermal debinding is simple and it can deal with the large quantity production easily.…”

Section: Introductionmentioning

confidence: 99%

Theory and practice of rapid and safe thermal debinding in ceramic injection molding

Xie

Jiang

Yang

et al. 2019

Int J Applied Ceramic Tech

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In this paper, the dynamic process of thermal debinding was analyzed. The critical thickness of debinding was defined as the thickness at which the steps to control dynamics change from diffusion of gas products in liquid binder to diffusion or permeation in pores. Subsequently, the equation of critical thickness was deduced. The results show that the critical thickness of debinding is independent of the thickness of the green body, but mainly depends on the particle size, solid content, and binder composition. Moreover, larger particle diameter and higher solid loading will contribute to a greater critical thickness, which means that higher heating rate can be used in the initial stage of debinding. The prediction is in agreement with the experimental results. In addition, the effect of binder composition on the formation of cracks during thermal debinding was investigated by thermogravimetry combined with FTIR spectrometry (TG-FTIR) analysis of binders and thermogravimetric curves of feedstocks. It suggests that the feedstock containing polystyrene and acrylic resin is helpful for rapid and safe thermal debinding. K E Y W O R D Sbinders/binding, ceramic engineering, defects, thermal debinding | 1099 XIE Et al.

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Injection molding of ultra-fine Si3N4 powder for gas-pressure sintering

Cited by 16 publications

References 24 publications

Comparative study of different alloys during thermal debind-ing of powder injection molded parts

Comparative study of different alloys during thermal debind-ing of powder injection molded parts

HPHT sintering of binderless Si3N4: structure, microstructure, mechanical properties and machining behavior

Theory and practice of rapid and safe thermal debinding in ceramic injection molding

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