br Experimental work br Results The samples were

Experimental work
Results The samples were friction welded. It can be seen from Fig. 6 that the heating time, upset time and interlayer thickness are the major criteria for joint performance. When the weld interfaces of Sample 13 were analyzed after experimentation, the friction and upset times were 1.2s and 6.5s, respectively. The macro examination of the fractured surface after the tensile test shows the major diffusion of copper on both the sides. For Sample 15, the heating and upset times were 1.2s and 7s, respectively. In this sample, the interlayer thickness was 0.65 mm, and the fractured surface reveals more copper diffused on the titanium alloy side and stainless steel side. Micro-hardness survey was done by Vickers hardness machine. The hardness values of the different samples are presented in Fig. 10. It is observed that the hardnesses of stainless steel varied between 271 VHN to 297 VHN which is more than that of membrane transport metal. The hardnesses of Ti alloy and copper vary from 298 VHN to 320 VHN and 77 VHN to 107 VHN, respectively. The tensile test results of different samples are listed in Table 6. 523.6 MPa tensile strength was obtained for 0.65 mm thick interlayer. The tensile strength reduces gradually as the interlayer thickness increases. The values of tensile strength ranges between 302.3 and 523.6 MPa. The diffusion of copper on both the sides of the joint is good and the tensile strength is remarkable with interlayer thickness between 0.65 and 0.85 mm.
Discussion
Conclusions A comparative study was performed to understand the friction welding characteristics of Ti–6Al–4V and SS304L with copper as interlayer and without interlayer. Based on the investigations performed, we conclude the following.
Acknowledgment
Introduction Conventional radar signal distribution networks are designed with coaxial cable or space-feeds, which make the system bulky, complex, massive and inflexible [1,2]. The inherent advantages of optical link is reduced size, weight and loss, low attenuation, immunity to electro-magnetic interference (EMI), and high bandwidth capacity [3]. Along with the advancements in microwave photonic device technology, the possibility for distribution of signals in optical domain had been opened up. During 1980\'s, the components capable of working in the microwave domain emerged. Pan [2] describes an optical link capable of working at 5 GHz. By 1984, a Ti: LiNbO3 Mach-Zehnder interferometer type external modulator capable of working at 17-GHz was developed to work in 830 nm [4]. In 1987, Stephens et al. [5] described a complete radio over fiber (RoF) link while comparing the performances of direct modulation and external modulation using loss, SNR (signal to noise ratio), linearity, etc., as the parameters for 4.1–4.7 GHz and 2.0–12.0 GHz. In 1988, the applications of radar X-band signal in fiber optic links were studied by a team in Malibu [6]. They were primarily interested in providing RF delay using fiber optic link for application in radar phase noise test set and radar repeater test. Link characterisation was also done for AM and FM modulations in direct and external modulations using 1300 nm InGaAs laser. Cox et al. [7] described an analytical lumped-element small-signal model of directly and externally modulated analog fiber optic link. The designed link was described to be superior to others in providing a maximum bandwidth of 22 MHz for externally modulated link (11 dB transducer gain, 6 dB noise figure) and 1 GHz bandwidth for directly modulated link (−14 dB transducer gain, 33 dB noise margin). They theoretically proved that the efficiency of externally modulated Mach-Zehnder modulator (MZM) operated at moderate bandwidth with high optical power is several times higher than that of direct modulation. Due to the versatility and practicality of optical links, soon results were available in introducing true time delays in phased array antennas [8]. The paper also provides a method to overcome beam squinting and describes the use of fiber delay loops in introducing a phase delay in microwave regime, which is expected to have a great impact on phased array antenna construction. It is only a matter of time that the optical system finds its way into the avionics industry, where light weight and immunity to EMI are highly desirable. Slaveski et al. [9] discussed the transmission of analog AM and FM signals over a WDM link along with FSK digital modulated signal between antennas and on-board avionic equipment. The results were promising with insertion loss of −55 dB, carrier to noise ratio (CNR) and SNR of more than 40 dB, total harmonic distortion (THD) of less than 7% and BER of more than 1.85e-07. This proves that the link works as efficiently as coaxial cable in antenna-cockpit link with the additional benefits of WDM optical systems.