The role of alloying elements on the sintering of Cu

doi:10.1016/j.jallcom.2016.05.143

Journal of Alloys and Compounds

Volume 684, 5 November 2016, Pages 91-97

https://doi.org/10.1016/j.jallcom.2016.05.143 Get rights and content

Highlights

•
A systematic investigation of the influences of alloying elements on the sintering of Cu.
•
Greatly enhancing the sintering behaviors of Cu with the addition of small amount of alloying elements.
•
Revealing the mechanism of the enhancement of the sintering behaviors of Cu.
•
A useful guidance to selecting suitable activated elements for Cu-based composites used in electronic packaging industry.

Abstract

The influence of alloying elements on the sintering behaviors of Cu is investigated by using Cu green samples doped with 0.5 wt% of Cr, Ti, Al, Mo, Nb and W. The sintering of Cu is greatly promoted by adding Cr, Ti and Al, but impeded by adding Mo, Nb and W. Among all alloying elements, Cr shows the most significant promoting effect, with the relative density of the Cu-0.5 wt% Cr sample being increased to 95% after sintering, about 5% higher than the pure Cu sample. Both the thermodynamic analysis and microstructure observation of the sintered samples suggest that the sintering enhancement can be attributed to the reduction of oxide layer on the Cu powder. The sintering-promoting elements are more affinitive to oxygen. Therefore, they are more likely to react with the oxide layer on the powder surface and facilitate the sintering.

Introduction

Cu-Diamond composites have been regarded to be the next generation of thermal management materials. In order to decrease the interfacial thermal resistance (ITR) between the Al matrix and the diamond particles, alloying elements are used either to dope the Cu matrix or to coat the diamond particles before the Cu and diamond are incorporated [1], [2], [3], [4]. Most alloying elements, such as Ti, Cr, Mo, W, Al and Nb, can form strong carbides with diamonds. The formed carbides exist as an intermediate layer between Cu and diamonds, improving their interfacial bonding and thus resulting in enhanced thermal properties [5], [6], [7], [8], [9].

The influences of alloying elements on the interfacial bonding and thermal conductivity (TC) of Cu-Diamond composites have been extensively investigated [10], [11], [12]. Shen et al. [5] reported that Mo coating can react with diamond particles to form nano-sized Mo₂C, which significantly increases the TC of the composites to 726 W/(m·K). Schubert et al. [13] found that premixed Cr in the Cu-diamond composite can form a thin layer of Cr₃C₂ along the Cu/Diamond interface in the subsequent pulse plasma sintering, therefore increasing the TC to 640 W/(m·K) and reducing the coefficient of thermal expansion (CTE) to ∼9 ppm/K. Apart from that, the reactivity between the alloying elements and the diamonds have also been widely studied. Sung et al. [14] found those elements used in the diamond cultivation industry as catalysts, such as Co, Fe, Mn, Ni and Cr, are most likely to react with diamonds. Tillman et al. [15] suggested that the carbon reactivity of metals is strongly linked to their electron configuration and decreases with increasing number of electrons in the d-orbit of the element.

However, as an important issue, the role of those alloying elements on the sintering behaviors of the Cu received little attention; although many studies in other alloy systems have already shown that trace amount of alloying elements may have significant effects on the sintering process. For example, small amount of B and P can facilitate the sintering of Fe by increasing the liquid phase in the sintering material [16]. In the sintering of Al single bond Cu alloys, trace amount of Sn can effectively improve the sintering by prolonging the liquid sintering time [17], [18]. The sinterability of WCu powder compacts can be increased by adding a small amount of Co, Ni, or Fe, which form compounds or agglomerate along the grain-boundaries to enhance self-diffusion and inter-diffusion between W atoms and Cu atoms [19], [20], [21]. Similarly, sintering of Mo can be improved by doping Mo with Ni, which forms δ-NiMo in which the diffusion rate of Mo atoms is 26,000 times faster than the self-diffusion rate of Mo, thus providing a short-circuit diffusion path for the sintering [22].

Therefore, it is reasonable to expect that the alloying elements added to Cu-diamond composites will influence the sintering process of the Cu matrix somehow. However, little work has been done to investigate the influences. Our previous research indicates that small amount of W and Ti, two most effective activated elements for Cu-Diamond composites, exhibit totally different effects on the sintering of Cu [23]. While Ti facilitates the sintering of Cu, W hampers its sintering. In this paper, the effects of more alloying elements on the sintering of Cu are investigated. The mechanisms of their influences are also fathomed, which provides a better understanding of the problem and can serve as a useful guidance to selecting suitable activated elements for Cu-diamond composites.

Section snippets

Experimental

Elemental powders of Cu, Al, Ti, Cr, Nb, Mo and W were used as raw materials in the research. The characteristics and microstructures of the powders are shown in Table 1 and Fig. 1, respectively. Powder mixtures of Cu-0.5 wt% X (X = Al, Ti, Cr, Nb, Mo or W) were blended in a tubular mixer (Sinomix Sci. & Tech. Co.) for 5 h with ethanol being used as a dispersing agent. The powder mixtures were subsequently cold-compacted under 400 MPa in a floating die to produce cylindrical green samples with

Results and discussions

Fig. 2 shows the dilatometric curves of green samples of pure Cu and those doped with 0.5 wt% of Al, Ti, Cr, Nb, Mo or W. All samples experience an expansion from room temperature to 500 °C. The slope of the dilatometric curves of all the samples in this temperature region is ∼16 ppm/°C, which is approximately equal to the CTE of pure Cu (16.7 ppm/°C). This indicates that the expansion of the samples at the early stage of heating is due to thermal expansion of Cu, and the effect of sintering is

Conclusions

Small amount (0.5 wt%) of alloying elements (Cr, Ti, Al, Mo, Nb and W) were added into the Cu. Cylindrical green samples were fabricated through cold pressing and their sintering behaviors were investigated using dilatometry. It is found that the addition of Cr, Ti and Al can promote the sintering of Cu, but the addition of Mo, Nb and W impedes the sintering. Cr exhibits the most sintering-promoting effect among all alloying elements. After sintering, the relative density of the Cu-0.5% Cr

Acknowledgements

This work is supported by the Project of Shenzhen Science and Technology (JCYJ20140417105742715) in China and Peacock Plan of Shenzhen (20130701226B).

References (29)

H.T. Wang et al.
Surf. Coat. Technol.
(2014)
L. Weber et al.
Scr. Mater.
(2007)
X.Y. Shen et al.
J. Alloys Comp.
(2012)
M. Vetterli et al.
Scr. Mater.
(2011)
J. Hell et al.
Surf. Coat. Technol.
(2012)
A.M. Abyzov et al.
Appl. Therm. Eng.
(2012)
A.M. Abyzov et al.
Mater. Des.
(2015)
K. Raza et al.
J. Alloys Comp.
(2014)
C. Zhao et al.
Mater. Sci. Eng. A
(2013)
T. Schubert et al.
Scr. Mater
(2008)

C.M. Sung et al.

Int. J. Refract. Met. Hard Mater

(1997)

W. Tillmann et al.

Diam. Relat. Mater.

(2013)

K.S. Hwang et al.

Acta Mater

(2003)

H. Hao et al.

J. Alloys Comp.

(2016)

Cited by (18)

Novel function-structure-integrated Ti-Mo-Cu alloy combined with excellent antibacterial properties and mechanical compatibility as implant application
2023, Journal of Alloys and Compounds
Ti-15Mo alloys have been widely used as biomedical materials. However, problems such as stress shielding and peri-implant infection occur when Ti-15Mo alloys are implanted in vivo. In this study, the function-structure-integrated Ti-15Mo-xCu (x = 3, 7, 11 and 15 wt%) alloys were prepared by powder metallurgy using Ti, Mo and Cu powders as raw materials. The results revealed that the Ti-15Mo-xCu alloys were mainly composed of β-Ti, α-Ti and Ti₂Cu phases. The Ti₂Cu phase combined with α-Ti formed a layer phase at the grain boundary. The strength of Ti-15Mo-xCu alloys decreased with Cu content increasing. When the Cu content was 11 wt%, the Ti-Mo-Cu alloy exhibited the higher compressive strength of 318.8 MPa and the lowest elastic modulus of 5.2 GPa. Simultaneously, the concentration of Cu ion release was proportional to the Cu content, which further affected the antibacterial activity. A high concentration of Cu ions was released from the alloys, and then became stable. Antibacterial rates of S. aureus and E. coli beyond 95% with good cytocompatibility can be obtained for the Ti-15Mo-11Cu alloy. This research revealed that the Ti-15Mo-11Cu alloy has excellent mechanical compatibility and antibacterial properties, which could satisfy the requirement for implant of human cortical bones.
Experimental investigation of hardness and impact toughness of in suit Ag-rich binder phase formation with h-BN/CuSn<inf>10</inf> metal matrix composite
2021, Journal of Alloys and Compounds
Citation Excerpt :
Alloying elements can react with the matrix at an interface, thereby effectively improving the bonding strength and properties of the matrix. Haoet et al. [14] studied the effects of different alloying elements on the sintering behavior of Cu. The study demonstrated that the interfacial reactions between Cr, Ti, Al, and the Cu matrix during sintering, formed Cr-O-Cu, Ti-Cu, and Al-O-Cu phases, improving the binding between the alloy and the matrix and promoting the sintering of Cu.
In order to improve the impact toughness of h-BN/CuSn₁₀ composites, and to realize their industrial application in urban rail transit, we prepared Ag/h-BN/CuSn₁₀ composites containing 3 wt% Ag using a powder metallurgy process. The microstructure of the composite was characterized by scanning electron microscopy, electron probe microanalysis, and energy dispersive spectroscopy. The transformation of the Ag-rich phase was recorded using confocal microscopy. The experimental results show that the Ag-rich binder phase, formed during the sintering process, promoted the dissolution and rearrangement of matrix particles, simultaneously filling the matrix pores. Thus, the continuity of the matrix was effectively improved, and the porosity of the composite material was significantly reduced. Compared with the original pristine composite, the relative density of the Ag/h-BN/CuSn₁₀ composite increased from 86 to 93%, and the impact toughness significantly increased from 2.9 to 8.4 J/cm², a 189% improvement.
Structure property relationship in a bulk Cu–Cr–W composite synthesized by high-energy ball milling and spark plasma sintering
2020, Materials Chemistry and Physics
Nanostructured Cu₉₈Cr₂–W composite powder was synthesized by high-energy ball milling and consolidated by spark plasma sintering (SPS). For comparison, pure Cu and Cu₉₈Cr₂ composite were also prepared under similar condition. Phase and microstructural characterization was carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Hardness, wear property and electrical conductivity of the composite was evaluated and compared with pure Cu and Cu₉₈Cr₂ composite. The Cu₉₈Cr₂–W composite, show ~5% and ~21% higher hardness compared to Cu₉₈Cr₂ and pure Cu respectively. It also shows significant improvement in wear property and electrical conductivity, which makes the newly developed composite a potentially better candidate for high voltage circuit breaker application over existing Cu–Cr based composites.
Interfacial microstructure and mechanical properties of Ti/Cu joint manufactured by Ni-Al thermal explosion reaction
2020, Journal of Manufacturing Processes
Citation Excerpt :
The three dimensionally interconnected pore channels are pinched off, leading to closed pore. The characteristics of the spheroidized voids can be seen from Fig. 10d. Based on the literatures [34–36], the relative density of Cu compact (Cu powder, 10∼30 μm, compacted under 400 MPa) is about 90 % when sintered at 800∼950 °C for 1∼2 h, indicating that there are still pores existed. Fig. 11 shows the microhardness of Ti/NiAl/Cu joint obtained at 600, 700, 800 and 900 °C for 30 min.
The dissimilar metals joining of Ti/Cu was conducted using a rapid thermal explosion (TE) reaction. The Ni-Al powder mixture was used as TE reaction system, and the effect of temperature (600, 700, 800 and 900 °C) on interfacial diffusions, microstructure and mechanical properties of Ti/Cu joint were investigated. The maximum combustion temperature of Ni-Al interlayer during heating process was 720 °C and a significant exothermic phenomenon was observed for 5 s. The infiltration of melted Al into the Ti/Cu substrate and formed a continuous transition region at the interface of the joints were the dominant joining mechanisms. Microhardness of the interlayer after heated at 900 °C for 30 min possessed prominent improvement from 32.6 to 101.7 HV due to the completely phase transformation of Ni-Al interlayer, which composed of main phase NiAl and minor phase Ni₃Al. The bond strength of the joint was checked to assess the joint quality. For the joint processed by 900 °C for 30 min, the maximum shear strength of Ti/NiAl and Cu/NiAl were 33.4 MPa and 39 MPa, respectively.
High-temperature pre-sintering: A new strategy to improve the properties of h-BN/CuSn<inf>10</inf> matrix composites
2020, Journal of Alloys and Compounds
Citation Excerpt :
Finally, the DSC curve of the MnNi/h-BN mixture is generally similar to that of the Mn/h-BN mixture; however, the temperature of the former shifts lower with the addition of Ni to the latter. Sintering behaviour can be improved by the addition of alloying elements via activated sintering [29,47–49]. As a result, the TMs Mn and Ni must benefit the activation of h-BN, and may reduce the sintering temperature and improve the density of the composites.
This study successfully introduced a pre-sintering process for the preparation of copper matrix composites and improved the combination of h-BN and the metal matrix. The effects of adding Mn and Ni in the pre-sintering of h-BN and their functionalization during pre-sintering were investigated. Our results show that h-BN was activated by introducing hydroxyl groups onto its surface after pre-sintering. A Mn₃(BO₃)₂ glass phase was formed by the reaction between Mn and activated h-BN, which filled the pores via viscous flow and decreased the porosity of the composite. Furthermore, the addition of Ni reduced the pre-sintering reaction temperature. Thus, the relative density of the pre-sintered h-BN/CuSn₁₀ composite was increased to 90.7% compared to that of the pristine original. The tensile strength and impact toughness of the former demonstrated significant improvement, by 26% and 168% respectively, to 156 MPa and 7.5 J/cm², respectively.
Sintering mechanism of Cu-9Al alloy prepared from elemental powders
2019, Progress in Natural Science: Materials International
Citation Excerpt :
Shaik et al. [11] studied the effect of hot pressing on the density and microstructure of Cu-15Al alloys and found that the density of the Cu-Al alloy reaches maximum (94.5%) density at 500 °C at a pressure of 500 MPa and the alloy consisted of Al4Cu9 and α-Cu phases. Hao et al. [12] studied the sintering behaviors of Cu-0.5% Al. An Al-rich phase was only present at the Cu grain boundaries at 950 °C, and oxygen was enriched at the matrix/additive boundary.
The sintering behavior of Cu-9Al alloys prepared from die pressing of elemental powders was investigated. The experimental results and kinetic analysis showed the formation of three consecutive layers of Al₂Cu, Al₄Cu₉, and AlCu phases, with Al₂Cu appearing first in the initial solid phase sintering stage. A liquid phase formed in the intermediate stage, resulting from the eutectic reaction between Al and Al₂Cu phases at 500 °C, which is 47 °C lower than the equilibrium reaction temperature. Swelling occurred when the liquid phase infiltrated the gaps between the copper particles, leaving pores at the original sites of Al particles and Al₂Cu. In the final stage of sintering, the Al-rich phases (Al₂Cu and AlCu) transformed to Al-poor phases (Al₄Cu₉ and α-Cu) in the temperature range of 500–565 °C. Al₄Cu₉ and α-Cu then transformed to AlCu₃ (β) above the eutectoid reaction temperature (565 °C), whereas AlCu₃ transformed to α-Cu and eutectoid phases (α-Cu + Al₄Cu₉) during cooling. The pure copper transformed to AlCu₃, and the pore volume decreased at 1000 °C. The microstructure study helps manipulate precisely the sintering process of Cu-Al alloys and optimize the microstructure with a high dimensional accuracy.

View all citing articles on Scopus

View full text

The role of alloying elements on the sintering of Cu

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussions

Conclusions

Acknowledgements

Surf. Coat. Technol.

Scr. Mater.

J. Alloys Comp.

Scr. Mater.

Surf. Coat. Technol.

Appl. Therm. Eng.

Mater. Des.

J. Alloys Comp.

Mater. Sci. Eng. A

Scr. Mater

Int. J. Refract. Met. Hard Mater

Diam. Relat. Mater.

Acta Mater

J. Alloys Comp.