Journal Published Online: 17 June 2019
Volume 8, Issue 5

Diffusion Bonding of Ti6Al4V and SS 304 with Nb Interlayer

CODEN: MPCACD

Abstract

In this investigation, solid-state indirect diffusion couples (IDCs) were prepared between stainless steel (SS) 304 and Ti6Al4V using a niobium (Nb) interlayer of 200 µm thickness from 850°C to 950°C using uniaxial compressive pressure (∼4 MPa) for 60 min under high vacuum of 10−3 Pa. Microstructural analysis along the Nb|SS-304 interfaces of IDCs processed at 875°C–950°C revealed layer-wise iron–niobium-based intermetallics like Fe2Nb and FeNb + (Nb), apart from these reaction layers IDCs processed at 925°C revealed a (Nb) reaction layer, and IDCs processed at 950°C revealed both (Nb) and γFe + σ reaction layers. IDCs processed at all processing temperatures revealed solid solution behavior along Ti6Al4V|Nb interfaces. Thermodynamic analysis showed that the diffusion mechanism at the Ti6Al4V|Nb interface is quite functionally easier than the diffusion mechanism observed at the Nb|SS-304 interface. Empirical atomic diffusivity (D) characteristics of Nb|SS-304 interface and Ti6Al4V|Nb interfaces are ∼1.957 × 10−14 m2/s and ∼9.197 × 10−14 m2/s, respectively, for the IDCs processed at 950°C. The observed maximum hardness at the Ti6Al4V|Nb interface was ∼300 HV; whereas hardness at the Nb|SS-304 interface is found to be ∼200 HV and ∼650 HV for IDCs processed at 850°C and at 875°C and above, respectively. A maximum strength of ∼372 MPa (tensile) and ∼241 MPa (shear), along with ∼4.5 % ductility, was noticed for the IDCs processed at 875°C. The presence of two reaction layers: FeNb + (Nb) and Fe2Nb at the Nb|SS-304 interfaces improved the strength properties of the IDCs. Strength properties of the IDCs processed at 950°C deteriorated because of the presence of σ phase. Using diffraction studies, hardness property, and fracture behavior, it was established that the IDCs failed because of the propagation of crack, apparently along iron–niobium-based intermetallic reaction layers at Nb|SS-304 interfaces.

Author Information

Thirunavukarasu, Gopinath
Department of Metallurgy and Materials Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, West Bengal, India
Patel, Vivek V.
The Shaanxi Key Laboratory of Friction Welding Technologies, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, Shaanxi, People’s Republic of China
Kundu, Sukumar
Department of Metallurgy and Materials Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, West Bengal, India
Alankar, Alankar
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, Maharashtra, India
Pages: 24
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Stock #: MPC20190041
ISSN: 2379-1365
DOI: 10.1520/MPC20190041