Densification behavior of copper powder during the coupled multi-physics fields-activated microforming

Abstract

External electric field-activated sintering techniques have been widely investigated and applied for the forming of large-sized components. These techniques are, however, rarely utilized for the manufacture of miniature and microsized components. In this paper, a novel, coupled forming, and sintering method is reported, which has been used for the fabrication of microcomponents, wherein the loose powder is loaded directly into the die, followed by simultaneous electrical forming and electric sintering (named coupled multi-physics-fields activation). In the study, the gears with the module of 0.2 and the pitch diameter of 1.6 mm were formed from copper powder. The coupled multi-fields activations were enabled using a Gleeble-1500D thermal simulation machine. Sintered samples with a relative density of 97.20 % have been fabricated at a sintering temperature of 700 °C, heating rate of 50 °C/s, forming pressure of 100 MPa, while these parameters were applied cyclically. The study showed that the axial reduction of the samples increased rapidly with the increase of temperature during the sintering, while the external pressure was maintained. Based on the experimental observations, it can be concluded that the deformation of the particles resulted in an increase in, and then subsequent disappearance of, the interface areas among the particles, which feature plays a key role in the densification of the copper powder

Sintering Kinetics of the Powder during Fields-Activated Micro-Forming and Sintering (Micro-FAST) of Copper Micro-Gears

“…This period is defined as the main densification realized process where the axial reduction increases rapidly (from -2.9553 mm to -3.3455 mm) with the temperature rising, which is shown in Fig.3. It is worth mentioning that there was a very obvious axial shrinkage of sample that occurred, which is a result of deformation and interface melting of particles and has been noted by authors [5,6,11]. (iv).…”

“…A novel micro-forming technology, named Micro-FAST (combining micro-forming and FAST), was proposed recently by the present authors for the forming of micro-components. Gears made of 316L stainless and Cu powder at the micro-scale have been fabricated successfully [5,6]. As the process illustrated in Fig.1, Micro-FAST is a method which can be used for the forming of micro-components with a variety of material systems, for instance, metals, ceramics and composites.…”

Effect of soaking time on the preparation of porous NiTi alloy during fields-activated micro-sintering and forming technology

“…Figure 1 shows the schematic of Micro-FAST. It has been used for the preparation of components with a variety of material systems, such as copper [10], 316 L stainless [11] and WC-Co composites [12]. It has been confirmed that Micro-FAST is a faster and simpler technology to fabricate micro-parts.…”

A new densification mechanism of copper powder sintered under an electrical field

“…To address this issue, a novel microforming technology, named Micro-FAST (combining microforming and field-activated sintering technology (FAST)), was proposed recently by the present authors for the forming of microcomponents [2][3][4][5]: the process is illustrated in Figure 1. Micro-FAST is a method which can be used for the forming of microcomponents with a variety of material systems, e.g.…”

“…Moreover, with continuous high pressures being applied and the short forming time, Micro-FAST occurs without coarsening of grains during the densification process [4]. Joule heating is the main heat source during the sintering process, and thus the process has different densification mechanisms compared to those of conventional processes (including FAST or spark plasma sintering (SPS)).…”